RE: [PATCH v18 5/5] remoteproc: Add initial zynqmp R5 remoteproc driver

[Ben Levinsky]

Hi Stefano,

Thanks for the review.

> -----Original Message-----
> From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
> Sent: Monday, October 19, 2020 1:44 PM
> To: Ben Levinsky <BLEVINSK@xxxxxxxxxx>
> Cc: Ed T. Mooring <emooring@xxxxxxxxxx>; sunnyliangjy@xxxxxxxxx;
> punit1.agrawal@xxxxxxxxxxxxx; Stefano Stabellini <stefanos@xxxxxxxxxx>;
> Michal Simek <michals@xxxxxxxxxx>; michael.auchter@xxxxxx;
> devicetree@xxxxxxxxxxxxxxx; mathieu.poirier@xxxxxxxxxx; linux-
> remoteproc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> robh+dt@xxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v18 5/5] remoteproc: Add initial zynqmp R5 remoteproc
> driver
> 
> On Mon, 5 Oct 2020, Ben Levinsky wrote:
> > R5 is included in Xilinx Zynq UltraScale MPSoC so by adding this
> > remotproc driver, we can boot the R5 sub-system in different 2
> > configurations -
> > 	* split
> > 	* lock-step
> >
> > The Xilinx R5 Remoteproc Driver boots the R5's via calls to the Xilinx
> > Platform Management Unit that handles the R5 configuration, memory
> access
> > and R5 lifecycle management. The interface to this manager is done in this
> > driver via zynqmp_pm_* function calls.
> 
> Mostly minor comments left
> 
> 
> > Signed-off-by: Wendy Liang <wendy.liang@xxxxxxxxxx>
> > Signed-off-by: Michal Simek <michal.simek@xxxxxxxxxx>
> > Signed-off-by: Ed Mooring <ed.mooring@xxxxxxxxxx>
> > Signed-off-by: Jason Wu <j.wu@xxxxxxxxxx>
> > Signed-off-by: Ben Levinsky <ben.levinsky@xxxxxxxxxx>
> > ---
> > v2:
> >  - remove domain struct as per review from Mathieu
> > v3:
> >  - add xilinx-related platform mgmt fn's instead of wrapping around
> >    function pointer in xilinx eemi ops struct
> > v4:
> >  - add default values for enums
> >  - fix formatting as per checkpatch.pl --strict. Note that 1 warning and 1
> check
> >    are still raised as each is due to fixing the warning results in that
> >  particular line going over 80 characters.
> > v5:
> >  - parse_fw change from use of rproc_of_resm_mem_entry_init to
> >  rproc_mem_entry_init and use of alloc/release
> >  - var's of type zynqmp_r5_pdata all have same local variable name
> >  - use dev_dbg instead of dev_info
> > v6:
> >  - adding memory carveouts is handled much more similarly. All mem
> >  carveouts are
> >    now described in reserved memory as needed. That is, TCM nodes are not
> >    coupled to remoteproc anymore. This is reflected in the remoteproc R5
> >  driver
> >    and the device tree binding.
> >  - remove mailbox from device tree binding as it is not necessary for elf
> >    loading
> >  - use lockstep-mode property for configuring RPU
> > v7:
> >  - remove unused headers
> >  - change  u32 *lockstep_mode ->  u32 lockstep_mode;
> >  - change device-tree binding "lockstep-mode"  to xlnx,cluster-mode
> >  - remove zynqmp_r5_mem_probe and loop to Probe R5 memory devices at
> >    remoteproc-probe time
> >  - remove is_r5_mode_set from  zynqmp rpu remote processor private data
> >  - do not error out if no mailbox is provided
> >  - remove zynqmp_r5_remoteproc_probe call of platform_set_drvdata as
> >  pdata is
> >    handled in zynqmp_r5_remoteproc_remove
> > v8:
> >  - remove old acks, reviewed-by's in commit message
> > v9:
> > - as mboxes are now optional, if pdata->tx_mc_skbs not initialized then
> >   do not call skb_queue_empty
> > - update usage for zynqmp_pm_set_rpu_mode,
> zynqmp_pm_set_tcm_config and
> >   zynqmp_pm_get_rpu_mode
> > - update 5/5 patch commit message to document supported configurations
> >   and how they are booted by the driver.
> > - remove copyrights other than SPDX from zynqmp_r5_remoteproc.c
> > - compilation warnings no longer raised
> > - remove unused includes from zynqmp_r5_remoteproc.c
> > - remove unused  var autoboot from zynqmp_r5_remoteproc.c
> > - reorder zynqmp_r5_pdata fpr small mem savings due to alignment
> > - use of zynqmp_pm_set_tcm_config now does not have
> >   output arg
> > - in tcm handling, unconditionally use &= 0x000fffff mask since all nodes
> >   in this fn are for tcm
> > - update comments for translating dma field in tcm handling to device
> >   address
> > - update calls to rproc_mem_entry_init in parse_mem_regions so that there
> >   are only 2 cases for types of carveouts instead of 3
> > - in parse_mem_regions, check if device tree node is null before using it
> > - add example device tree nodes used in parse_mem_regions and tcm
> parsing
> > - add comment for vring id node length
> > - add check for string length so that vring id is at least min length
> > - move tcm nodes from reserved mem to instead own device tree nodes
> >    and only use them if enabled in device tree
> > - add comment for explaining handling of rproc_elf_load_rsc_table
> > - remove obsolete check for "if (vqid < 0)" in zynqmp_r5_rproc_kick
> > - remove unused field mems in struct zynqmp_r5_pdata
> > - remove call to zynqmp_r5_mem_probe and the fn itself as tcm handling
> >   is done by zyqmp_r5_pm_request_tcm
> > - remove obsolete setting of dma_ops and parent device dma_mask
> > - remove obsolete use of of_dma_configure
> > - add comment for call to r5_set_mode fn
> > - make mbox usage optional and gracefully inform user via dev_dbg if not
> >   present
> > - change var lockstep_mode from u32* to u32
> > v11:
> > - use enums instead of u32 where possible in zynqmp_r5_remoteproc
> > - update usage of zynqmp_pm_set/get_rpu_mode and
> zynqmp_pm_set_tcm_config
> > - update prints to not use carriage return, just newline
> > - look up tcm banks via property in r5 node instead of string name
> > - print device tree nodes with %pOF instead of %s with node name field
> > - update tcm release to unmap VA
> > - handle r5-1 use case
> > v12:
> > - update signed off by so that latest developer name is last
> > - do not cast enums to u32s for zynqmp_pm* functions
> > v14:
> > - change zynqmp_r5_remoteproc::rpus and rpu_mode to static
> > - fix typo
> > - zynqmp_r5_remoteproc::r5_set_mode set rpu mode from
> >   property specified in device tree
> > - use u32 instead of u32* to store in remoteproc memory entry private data
> >   for pnode_id information
> > - always call r5_set_mode on probe
> > - remove alloc of zynqmp_r5_pdata in
> >   zynqmp_r5_remoteproc::zynqmp_r5_remoteproc_probe as there is static
> >   allocation already
> > - error at probe time if lockstep-mode property not present in device tree
> > - update commit message as per review
> > - remove dependency on MAILBOX in makefile as ZYNQMP_IPI_MBOX is
> present
> > - remove unused macros
> > - update comment ordering of zynqmp_r5_pdata to match struct definition
> > - zynqmp_r5_remoteproc::tcm_mem_release error if pnode id is invalid
> > - remove obsolete TODOs
> > - only call zynqmp_r5_remoteproc::zynqmp_r5_probe if the index is valid
> > - remove uneven dev_dbg/dev_err fn calls
> > v15:
> > - if lockstep mode prop is present, then RPU cluster is in lockstep mode.
> >   if not present, cluster is in split mode.
> > - if 2 RPUs provided but one is lockstep then error out as this is invalid
> >   configuration
> > v16:
> > - replace of_get_property(dev->of_node, "lockstep-mode" with
> >   of_property_read_bool
> > - propagate rpu mode specified in device tree through functions instead
> >   of holding a global, static var
> > - check child remoteproc nodes via of_get_available_child_count before
> >   looping through children
> > - replace check of "pdata->pnode_id == 0" instead by checking rpu's
> >   zynqmp_r5_pdata* if NULL
> > - remove old, obsolete checks for dma_pools in
> zynqmp_r5_remoteproc_remove
> > - change rpus from zynqmp_r5_pdata[] to zynqmp_r5_pdata*[] so that
> >   check for pdata->pnode_id == 0 is not needed
> > v17:
> > - fix style as per kernel test bot
> > v18:
> > - to more closely mimic other remoteproc drivers, change zynqmp r5 rproc
> >   data from zynqmp_r5_pdata to zynqmp_r5_rproc and pdata local var to
> >   zproc
> > - remove global vars rpus and rpu_mode
> > - instantiate device for zynqmp r5 rproc from device set by rproc_alloc
> > - fix typos
> > - update to call zynqmp_r5_release from the rproc_alloc-related device and
> >   remove the instantiated device from zynqmp_r5_probe
> > - remove unneeded call to platform_set_drvdata
> > - remove driver remove function, as the clean up is handled in release
> > - remove while (!skb_queue_empty loop and mbox_free_channel calls in
> >   zynqmp_r5_release, and mbox_free_channel
> > - remove device_unregister call in zynqmp_r5_release
> > - remove kzalloc for pdata (what is now called z_rproc)
> > - update conditional in loop to calls of zynqmp_r5_probe
> >
> > ---
> >  drivers/remoteproc/Kconfig                |   8 +
> >  drivers/remoteproc/Makefile               |   1 +
> >  drivers/remoteproc/zynqmp_r5_remoteproc.c | 707
> ++++++++++++++++++++++
> >  3 files changed, 716 insertions(+)
> >  create mode 100644 drivers/remoteproc/zynqmp_r5_remoteproc.c
> >
> > diff --git a/drivers/remoteproc/Kconfig b/drivers/remoteproc/Kconfig
> > index c6659dfea7c7..68e567c5375c 100644
> > --- a/drivers/remoteproc/Kconfig
> > +++ b/drivers/remoteproc/Kconfig
> > @@ -275,6 +275,14 @@ config TI_K3_DSP_REMOTEPROC
> >  	  It's safe to say N here if you're not interested in utilizing
> >  	  the DSP slave processors.
> >
> > +config ZYNQMP_R5_REMOTEPROC
> > +	tristate "ZynqMP_R5 remoteproc support"
> > +	depends on PM && ARCH_ZYNQMP
> > +	select RPMSG_VIRTIO
> > +	select ZYNQMP_IPI_MBOX
> > +	help
> > +	  Say y or m here to support ZynqMP R5 remote processors via the
> remote
> > +	  processor framework.
> >  endif # REMOTEPROC
> >
> >  endmenu
> > diff --git a/drivers/remoteproc/Makefile b/drivers/remoteproc/Makefile
> > index 3dfa28e6c701..ef1abff654c2 100644
> > --- a/drivers/remoteproc/Makefile
> > +++ b/drivers/remoteproc/Makefile
> > @@ -33,3 +33,4 @@ obj-$(CONFIG_ST_REMOTEPROC)		+=
> st_remoteproc.o
> >  obj-$(CONFIG_ST_SLIM_REMOTEPROC)	+= st_slim_rproc.o
> >  obj-$(CONFIG_STM32_RPROC)		+= stm32_rproc.o
> >  obj-$(CONFIG_TI_K3_DSP_REMOTEPROC)	+= ti_k3_dsp_remoteproc.o
> > +obj-$(CONFIG_ZYNQMP_R5_REMOTEPROC)	+= zynqmp_r5_remoteproc.o
> > diff --git a/drivers/remoteproc/zynqmp_r5_remoteproc.c
> b/drivers/remoteproc/zynqmp_r5_remoteproc.c
> > new file mode 100644
> > index 000000000000..37bd76252ff2
> > --- /dev/null
> > +++ b/drivers/remoteproc/zynqmp_r5_remoteproc.c
> > @@ -0,0 +1,707 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Zynq R5 Remote Processor driver
> > + *
> > + * Based on origin OMAP and Zynq Remote Processor driver
> > + *
> > + */
> > +
> > +#include <linux/firmware/xlnx-zynqmp.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/kernel.h>
> > +#include <linux/list.h>
> > +#include <linux/mailbox_client.h>
> > +#include <linux/mailbox/zynqmp-ipi-message.h>
> > +#include <linux/module.h>
> > +#include <linux/of_address.h>
> > +#include <linux/of_platform.h>
> > +#include <linux/of_reserved_mem.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/remoteproc.h>
> > +#include <linux/skbuff.h>
> > +#include <linux/sysfs.h>
> > +
> > +#include "remoteproc_internal.h"
> > +
> > +#define MAX_RPROCS	2 /* Support up to 2 RPU */
> > +#define MAX_MEM_PNODES	4 /* Max power nodes for one RPU memory
> instance */
> > +
> > +#define BANK_LIST_PROP "meta-memory-regions"
> > +
> > +/* IPI buffer MAX length */
> > +#define IPI_BUF_LEN_MAX	32U
> > +/* RX mailbox client buffer max length */
> > +#define RX_MBOX_CLIENT_BUF_MAX	(IPI_BUF_LEN_MAX + \
> > +				 sizeof(struct zynqmp_ipi_message))
> > +
> > +/**
> > + * struct zynqmp_r5_mem - zynqmp rpu memory data
> > + * @pnode_id: TCM power domain ids
> > + * @res: memory resource
> > + * @node: list node
> > + */
> > +struct zynqmp_r5_mem {
> > +	u32 pnode_id[MAX_MEM_PNODES];
> > +	struct resource res;
> > +	struct list_head node;
> > +};
> > +
> > +/**
> > + * struct zynqmp_r5_rproc - zynqmp rpu remote processor state
> > + * @rx_mc_buf: rx mailbox client buffer to save the rx message
> > + * @tx_mc: tx mailbox client
> > + * @rx_mc: rx mailbox client * @dev: device of RPU instance
> > + * @mbox_work: mbox_work for the RPU remoteproc
> > + * @tx_mc_skbs: socket buffers for tx mailbox client
> > + * @dev: device of RPU instance
> > + * @rproc: rproc handle
> > + * @tx_chan: tx mailbox channel
> > + * @rx_chan: rx mailbox channel
> > + * @pnode_id: RPU CPU power domain id
> > + */
> > +struct zynqmp_r5_rproc {
> > +	unsigned char rx_mc_buf[RX_MBOX_CLIENT_BUF_MAX];
> > +	struct mbox_client tx_mc;
> > +	struct mbox_client rx_mc;
> > +	struct work_struct mbox_work;
> > +	struct sk_buff_head tx_mc_skbs;
> > +	struct device dev;
> > +	struct rproc *rproc;
> > +	struct mbox_chan *tx_chan;
> > +	struct mbox_chan *rx_chan;
> > +	u32 pnode_id;
> > +};
> > +
> > +/*
> > + * r5_set_mode - set RPU operation mode
> > + * @z_rproc: Remote processor private data
> > + *
> > + * set RPU operation mode
> > + *
> > + * Return: 0 for success, negative value for failure
> > + */
> > +static int r5_set_mode(struct zynqmp_r5_rproc *z_rproc,
> > +		       enum rpu_oper_mode rpu_mode)
> > +{
> > +	enum rpu_tcm_comb tcm_mode;
> > +	enum rpu_oper_mode cur_rpu_mode;
> > +	int ret;
> > +
> > +	ret = zynqmp_pm_get_rpu_mode(z_rproc->pnode_id,
> &cur_rpu_mode);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	if (rpu_mode != cur_rpu_mode) {
> > +		ret = zynqmp_pm_set_rpu_mode(z_rproc->pnode_id,
> > +					     rpu_mode);
> > +		if (ret < 0)
> > +			return ret;
> > +	}
> > +
> > +	tcm_mode = (rpu_mode == PM_RPU_MODE_LOCKSTEP) ?
> > +		    PM_RPU_TCM_COMB : PM_RPU_TCM_SPLIT;
> > +	return zynqmp_pm_set_tcm_config(z_rproc->pnode_id, tcm_mode);
> > +}
> > +
> > +/*
> > + * ZynqMP R5 remoteproc memory release function
> > + */
> > +static int tcm_mem_release(struct rproc *rproc, struct rproc_mem_entry
> *mem)
> > +{
> > +	u32 pnode_id = (u64)mem->priv;
> > +
> > +	if (pnode_id <= 0)
> 
> pnode_id is a u32, so checks for it to be negative don't make a lot of
> sense
> 
> 
Will fix in next rev
> > +		return -EINVAL;
> > +
> > +	iounmap(mem->va);
> > +	return zynqmp_pm_release_node(pnode_id);
> > +}
> > +
> > +/*
> > + * ZynqMP R5 remoteproc operations
> > + */
> > +static int zynqmp_r5_rproc_start(struct rproc *rproc)
> > +{
> > +	struct device *dev = rproc->dev.parent;
> > +	struct zynqmp_r5_rproc *z_rproc = rproc->priv;
> > +	enum rpu_boot_mem bootmem;
> > +
> > +	bootmem = (rproc->bootaddr & 0xF0000000) == 0xF0000000 ?
> > +		  PM_RPU_BOOTMEM_HIVEC : PM_RPU_BOOTMEM_LOVEC;
> > +
> > +	dev_dbg(dev, "RPU boot from %s.",
> > +		bootmem == PM_RPU_BOOTMEM_HIVEC ? "OCM" : "TCM");
> > +
> > +	return zynqmp_pm_request_wake(z_rproc->pnode_id, 1,
> > +				     bootmem,
> ZYNQMP_PM_REQUEST_ACK_NO);
> > +}
> > +
> > +static int zynqmp_r5_rproc_stop(struct rproc *rproc)
> > +{
> > +	struct zynqmp_r5_rproc *z_rproc = rproc->priv;
> > +	struct sk_buff *skb;
> > +
> > +	if (z_rproc->tx_chan)
> > +		mbox_free_channel(z_rproc->tx_chan);
> > +	if (z_rproc->rx_chan)
> > +		mbox_free_channel(z_rproc->rx_chan);
> > +
> > +	return zynqmp_pm_force_pwrdwn(z_rproc->pnode_id,
> > +				     ZYNQMP_PM_REQUEST_ACK_BLOCKING);
> > +}
> > +
> > +static int zynqmp_r5_rproc_mem_alloc(struct rproc *rproc,
> > +				     struct rproc_mem_entry *mem)
> > +{
> > +	void *va;
> > +
> > +	va = ioremap_wc(mem->dma, mem->len);
> > +	if (IS_ERR_OR_NULL(va))
> > +		return -ENOMEM;
> > +
> > +	/* Update memory entry va */
> > +	mem->va = va;
> > +
> > +	return 0;
> > +}
> > +
> > +static int zynqmp_r5_rproc_mem_release(struct rproc *rproc,
> > +				       struct rproc_mem_entry *mem)
> > +{
> > +	iounmap(mem->va);
> > +	return 0;
> > +}
> > +
> > +static int parse_mem_regions(struct rproc *rproc)
> > +{
> > +	int num_mems, i;
> > +	struct zynqmp_r5_rproc *z_rproc = rproc->priv;
> > +	struct device *dev =  &z_rproc->dev;
> > +	struct device_node *np = dev->of_node;
> > +	struct rproc_mem_entry *mem;
> > +
> > +	num_mems = of_count_phandle_with_args(np, "memory-region",
> NULL);
> > +	if (num_mems <= 0)
> > +		return 0;
> > +
> > +	for (i = 0; i < num_mems; i++) {
> > +		struct device_node *node;
> > +		struct reserved_mem *rmem;
> > +
> > +		node = of_parse_phandle(np, "memory-region", i);
> > +		if (!node)
> > +			return -EINVAL;
> > +
> > +		rmem = of_reserved_mem_lookup(node);
> > +		if (!rmem)
> > +			return -EINVAL;
> > +
> > +		if (strstr(node->name, "vdev0vring")) {
> > +			int vring_id;
> > +			char name[16];
> > +
> > +			/*
> > +			 * expecting form of "rpuXvdev0vringX as documented
> > +			 * in xilinx remoteproc device tree binding
> > +			 */
> > +			if (strlen(node->name) < 14) {
> > +				dev_err(dev, "%pOF is less than 14 chars",
> > +					node);
> > +				return -EINVAL;
> > +			}
> > +
> > +			/*
> > +			 * can be 1 of multiple vring IDs per IPC channel
> > +			 * e.g. 'vdev0vring0' and 'vdev0vring1'
> > +			 */
> > +			vring_id = node->name[14] - '0';
> 
> If you are going to use a direct access to node->name[14], then the
> strlen check above should cover it, which means we should check for at
> least strlen(node->name) < 15.
> 
Will fix in next rev

> 
> > +			snprintf(name, sizeof(name), "vdev0vring%d",
> vring_id);
> > +			/* Register vring */
> > +			mem = rproc_mem_entry_init(dev, NULL,
> > +						   (dma_addr_t)rmem->base,
> > +						   rmem->size, rmem->base,
> > +
> zynqmp_r5_rproc_mem_alloc,
> > +
> zynqmp_r5_rproc_mem_release,
> > +						   name);
> > +		} else {
> > +			/* Register DMA region */
> > +			int (*alloc)(struct rproc *r,
> > +				     struct rproc_mem_entry *rme);
> > +			int (*release)(struct rproc *r,
> > +				       struct rproc_mem_entry *rme);
> > +			char name[20];
> > +
> > +			if (strstr(node->name, "vdev0buffer")) {
> > +				alloc = NULL;
> > +				release = NULL;
> > +				strcpy(name, "vdev0buffer");
> > +			} else {
> > +				alloc = zynqmp_r5_rproc_mem_alloc;
> > +				release = zynqmp_r5_rproc_mem_release;
> > +				strcpy(name, node->name);
> > +			}
> > +
> > +			mem = rproc_mem_entry_init(dev, NULL,
> > +						   (dma_addr_t)rmem->base,
> > +						   rmem->size, rmem->base,
> > +						   alloc, release, name);
> > +		}
> > +		if (!mem)
> > +			return -ENOMEM;
> > +
> > +		rproc_add_carveout(rproc, mem);
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +/* call Xilinx Platform manager to request access to TCM bank */
> > +static int zynqmp_r5_pm_request_tcm(struct device_node *tcm_node,
> > +				    struct device *dev, u32 *pnode_id)
> > +{
> > +	int ret;
> > +
> > +	ret = of_property_read_u32(tcm_node, "pnode-id", pnode_id);
> > +	if (ret)
> > +		return ret;
> > +
> > +	return zynqmp_pm_request_node(*pnode_id,
> ZYNQMP_PM_CAPABILITY_ACCESS, 0,
> > +				     ZYNQMP_PM_REQUEST_ACK_BLOCKING);
> > +}
> > +
> > +/* Given tcm bank entry,
> 
> I think checkpatch.pl would complain for this comment format
> 
Will fix in next rev 
> 
> > + * this callback will set device address for R5 running on TCM
> > + * and also setup virtual address for tcm bank remoteproc carveout
> > + */
> > +static int tcm_mem_alloc(struct rproc *rproc,
> > +			 struct rproc_mem_entry *mem)
> > +{
> > +	void *va;
> > +	struct device *dev = rproc->dev.parent;
> > +
> > +	va = ioremap_wc(mem->dma, mem->len);
> > +	if (IS_ERR_OR_NULL(va))
> > +		return -ENOMEM;
> > +
> > +	/* Update memory entry va */
> > +	mem->va = va;
> > +
> > +	va = devm_ioremap_wc(dev, mem->da, mem->len);
> > +	if (!va)
> > +		return -ENOMEM;
> > +	/* As R5 is 32 bit, wipe out extra high bits */
> > +	mem->da &= 0x000fffff;
> > +	/*
> > +	 * handle tcm banks 1 a and b (0xffe90000 and oxffeb0000)
> > +	 * As both of these the only common bit found not in tcm bank0 a or
> b
> > +	 * is at 0x80000 use this mask to suss it out
> > +	 */
> > +	if (mem->da & 0x80000)
> > +		/*
> > +		 * need to do more to further translate
> > +		 * tcm banks 1a and 1b at 0xffe90000 and oxffeb0000
>                                                  ^typo
> 
> 
> > +		 * respectively to 0x0 and 0x20000
> > +		 */
> > +		mem->da -= 0x90000;
> 
> I understand now why we do "mem->da -= 0x90000" and the in-code
> comment
> explains it. However, why the "if (mem->da & 0x80000)" check?
> 
> If we want to make sure to do this "translation" only for 0xffe90000 and
> 0xffeb0000, wouldn't it be better to call them out explicitly, like:
> 
>   if (mem->da == 0x90000 || mem->da == 0xB0000)
> 
Good suggestion, will change if  as suggest 
> 
> Also if this if check fails, should we print an error? Or is it a
> possible handled condition?

Previously this is otherwise handled as TCM banks 0A and 0B. For completeness I will add error checking if it is not in this range either and if so, raise dev_err and EINVAL.

Thanks
Ben