Re: [PATCH v3 2/2] firmware: arm_scmi: Support 'reg-io-width' property for shared memory

From: Florian Fainelli
Date: Tue Aug 20 2024 - 12:35:12 EST

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On 8/19/24 19:49, Peng Fan wrote:

Subject: [PATCH v3 2/2] firmware: arm_scmi: Support 'reg-io-width'
property for shared memory

Some shared memory areas might only support a certain access width,
such as 32-bit, which memcpy_{from,to}_io() does not adhere to at
least on ARM64 by making both 8-bit and 64-bit accesses to such
memory.

Update the shmem layer to support reading from and writing to such
shared memory area using the specified I/O width in the Device Tree.
The various transport layers making use of the shmem.c code are
updated accordingly to pass the I/O accessors that they store.

Signed-off-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
---
drivers/firmware/arm_scmi/common.h | 32 ++++++-
.../arm_scmi/scmi_transport_mailbox.c | 13 ++-
.../firmware/arm_scmi/scmi_transport_optee.c | 11 ++-
.../firmware/arm_scmi/scmi_transport_smc.c | 11 ++-
drivers/firmware/arm_scmi/shmem.c | 86 +++++++++++++++++-
-
5 files changed, 132 insertions(+), 21 deletions(-)

diff --git a/drivers/firmware/arm_scmi/common.h
b/drivers/firmware/arm_scmi/common.h
index 69928bbd01c2..73bb496fac01 100644
--- a/drivers/firmware/arm_scmi/common.h
+++ b/drivers/firmware/arm_scmi/common.h
@@ -316,6 +316,26 @@ enum scmi_bad_msg {
MSG_MBOX_SPURIOUS = -5,
};

+/* Used for compactness and signature validation of the function
+pointers being
+ * passed.
+ */
+typedef void (*shmem_copy_toio_t)(volatile void __iomem *to, const
void *from,
+ size_t count);
+typedef void (*shmem_copy_fromio_t)(void *to, const volatile void
__iomem *from,
+ size_t count);
+
+/**
+ * struct scmi_shmem_io_ops - I/O operations to read from/write to
+ * Shared Memory
+ *
+ * @toio: Copy data to the shared memory area
+ * @fromio: Copy data from the shared memory area */ struct
+scmi_shmem_io_ops {
+ shmem_copy_fromio_t fromio;
+ shmem_copy_toio_t toio;
+};
+
/* shmem related declarations */
struct scmi_shared_mem;

@@ -336,13 +356,16 @@ struct scmi_shared_mem; struct
scmi_shared_mem_operations {
void (*tx_prepare)(struct scmi_shared_mem __iomem
*shmem,
struct scmi_xfer *xfer,
- struct scmi_chan_info *cinfo);
+ struct scmi_chan_info *cinfo,
+ shmem_copy_toio_t toio);
u32 (*read_header)(struct scmi_shared_mem __iomem
*shmem);

void (*fetch_response)(struct scmi_shared_mem __iomem
*shmem,
- struct scmi_xfer *xfer);
+ struct scmi_xfer *xfer,
+ shmem_copy_fromio_t fromio);
void (*fetch_notification)(struct scmi_shared_mem __iomem
*shmem,
- size_t max_len, struct scmi_xfer
*xfer);
+ size_t max_len, struct scmi_xfer
*xfer,
+ shmem_copy_fromio_t fromio);
void (*clear_channel)(struct scmi_shared_mem __iomem
*shmem);
bool (*poll_done)(struct scmi_shared_mem __iomem *shmem,
struct scmi_xfer *xfer);
@@ -350,7 +373,8 @@ struct scmi_shared_mem_operations {
bool (*channel_intr_enabled)(struct scmi_shared_mem
__iomem *shmem);
void __iomem *(*setup_iomap)(struct scmi_chan_info *cinfo,
struct device *dev,
- bool tx, struct resource *res);
+ bool tx, struct resource *res,
+ struct scmi_shmem_io_ops **ops);
};

const struct scmi_shared_mem_operations
*scmi_shared_mem_operations_get(void);
diff --git a/drivers/firmware/arm_scmi/scmi_transport_mailbox.c
b/drivers/firmware/arm_scmi/scmi_transport_mailbox.c
index dc5ca894d5eb..1a2e90e5c765 100644
--- a/drivers/firmware/arm_scmi/scmi_transport_mailbox.c
+++ b/drivers/firmware/arm_scmi/scmi_transport_mailbox.c
@@ -25,6 +25,7 @@
* @chan_platform_receiver: Optional Platform Receiver mailbox
unidirectional channel
* @cinfo: SCMI channel info
* @shmem: Transmit/Receive shared memory area
+ * @io_ops: Transport specific I/O operations
*/
struct scmi_mailbox {
struct mbox_client cl;
@@ -33,6 +34,7 @@ struct scmi_mailbox {
struct mbox_chan *chan_platform_receiver;
struct scmi_chan_info *cinfo;
struct scmi_shared_mem __iomem *shmem;
+ struct scmi_shmem_io_ops *io_ops;
};

#define client_to_scmi_mailbox(c) container_of(c, struct scmi_mailbox,
cl) @@ -43,7 +45,8 @@ static void tx_prepare(struct mbox_client *cl,
void *m) {
struct scmi_mailbox *smbox = client_to_scmi_mailbox(cl);

- core->shmem->tx_prepare(smbox->shmem, m, smbox->cinfo);
+ core->shmem->tx_prepare(smbox->shmem, m, smbox->cinfo,
+ smbox->io_ops->toio);
}

static void rx_callback(struct mbox_client *cl, void *m) @@ -197,7
+200,8 @@ static int mailbox_chan_setup(struct scmi_chan_info
*cinfo, struct device *dev,
if (!smbox)
return -ENOMEM;

- smbox->shmem = core->shmem->setup_iomap(cinfo, dev, tx,
NULL);
+ smbox->shmem = core->shmem->setup_iomap(cinfo, dev, tx,
NULL,
+ &smbox->io_ops);
if (IS_ERR(smbox->shmem))
return PTR_ERR(smbox->shmem);

@@ -298,7 +302,7 @@ static void mailbox_fetch_response(struct
scmi_chan_info *cinfo, {
struct scmi_mailbox *smbox = cinfo->transport_info;

- core->shmem->fetch_response(smbox->shmem, xfer);
+ core->shmem->fetch_response(smbox->shmem, xfer,
+smbox->io_ops->fromio);
}

static void mailbox_fetch_notification(struct scmi_chan_info *cinfo,
@@ -306,7 +310,8 @@ static void mailbox_fetch_notification(struct
scmi_chan_info *cinfo, {
struct scmi_mailbox *smbox = cinfo->transport_info;

- core->shmem->fetch_notification(smbox->shmem, max_len,
xfer);
+ core->shmem->fetch_notification(smbox->shmem, max_len,
xfer,
+ smbox->io_ops->fromio);
}

static void mailbox_clear_channel(struct scmi_chan_info *cinfo) diff --
git a/drivers/firmware/arm_scmi/scmi_transport_optee.c
b/drivers/firmware/arm_scmi/scmi_transport_optee.c
index 08911f40d1ff..2be4124c6826 100644
--- a/drivers/firmware/arm_scmi/scmi_transport_optee.c
+++ b/drivers/firmware/arm_scmi/scmi_transport_optee.c
@@ -114,6 +114,7 @@ enum scmi_optee_pta_cmd {
* @req.shmem: Virtual base address of the shared memory
* @req.msg: Shared memory protocol handle for SCMI request and
* synchronous response
+ * @io_ops: Transport specific I/O operations
* @tee_shm: TEE shared memory handle @req or NULL if using
IOMEM shmem
* @link: Reference in agent's channel list
*/
@@ -128,6 +129,7 @@ struct scmi_optee_channel {
struct scmi_shared_mem __iomem *shmem;
struct scmi_msg_payld *msg;
} req;
+ struct scmi_shmem_io_ops *io_ops;
struct tee_shm *tee_shm;
struct list_head link;
};
@@ -350,7 +352,8 @@ static int setup_dynamic_shmem(struct device
*dev, struct scmi_optee_channel *ch static int
setup_static_shmem(struct device *dev, struct scmi_chan_info *cinfo,
struct scmi_optee_channel *channel) {
- channel->req.shmem = core->shmem->setup_iomap(cinfo, dev,
true, NULL);
+ channel->req.shmem = core->shmem->setup_iomap(cinfo, dev,
true, NULL,
+ &channel-

io_ops);

if (IS_ERR(channel->req.shmem))
return PTR_ERR(channel->req.shmem);

@@ -465,7 +468,8 @@ static int scmi_optee_send_message(struct
scmi_chan_info *cinfo,
ret = invoke_process_msg_channel(channel,
core->msg-

command_size(xfer));

} else {
- core->shmem->tx_prepare(channel->req.shmem, xfer,
cinfo);
+ core->shmem->tx_prepare(channel->req.shmem, xfer,
cinfo,
+ channel->io_ops->toio);
ret = invoke_process_smt_channel(channel);
}

@@ -484,7 +488,8 @@ static void scmi_optee_fetch_response(struct
scmi_chan_info *cinfo,
core->msg->fetch_response(channel->req.msg,
channel->rx_len, xfer);
else
- core->shmem->fetch_response(channel->req.shmem,
xfer);
+ core->shmem->fetch_response(channel->req.shmem,
xfer,
+ channel->io_ops->fromio);
}

static void scmi_optee_mark_txdone(struct scmi_chan_info *cinfo, int
ret, diff --git a/drivers/firmware/arm_scmi/scmi_transport_smc.c
b/drivers/firmware/arm_scmi/scmi_transport_smc.c
index c6c69a17a9cc..04e715ec1570 100644
--- a/drivers/firmware/arm_scmi/scmi_transport_smc.c
+++ b/drivers/firmware/arm_scmi/scmi_transport_smc.c
@@ -45,6 +45,7 @@
* @irq: An optional IRQ for completion
* @cinfo: SCMI channel info
* @shmem: Transmit/Receive shared memory area
+ * @io_ops: Transport specific I/O operations
* @shmem_lock: Lock to protect access to Tx/Rx shared memory area.
* Used when NOT operating in atomic mode.
* @inflight: Atomic flag to protect access to Tx/Rx shared memory
area.
@@ -60,6 +61,7 @@ struct scmi_smc {
int irq;
struct scmi_chan_info *cinfo;
struct scmi_shared_mem __iomem *shmem;
+ struct scmi_shmem_io_ops *io_ops;
/* Protect access to shmem area */
struct mutex shmem_lock;
#define INFLIGHT_NONE MSG_TOKEN_MAX
@@ -144,7 +146,8 @@ static int smc_chan_setup(struct
scmi_chan_info *cinfo, struct device *dev,
if (!scmi_info)
return -ENOMEM;

- scmi_info->shmem = core->shmem->setup_iomap(cinfo, dev,
tx, &res);
+ scmi_info->shmem = core->shmem->setup_iomap(cinfo, dev,
tx, &res,
+ &scmi_info-

io_ops);

if (IS_ERR(scmi_info->shmem))
return PTR_ERR(scmi_info->shmem);

@@ -229,7 +232,8 @@ static int smc_send_message(struct
scmi_chan_info *cinfo,
*/
smc_channel_lock_acquire(scmi_info, xfer);

- core->shmem->tx_prepare(scmi_info->shmem, xfer, cinfo);
+ core->shmem->tx_prepare(scmi_info->shmem, xfer, cinfo,
+ scmi_info->io_ops->toio);

if (scmi_info->cap_id != ULONG_MAX)
arm_smccc_1_1_invoke(scmi_info->func_id,
scmi_info->cap_id, 0, @@ -253,7 +257,8 @@ static void
smc_fetch_response(struct scmi_chan_info *cinfo, {
struct scmi_smc *scmi_info = cinfo->transport_info;

- core->shmem->fetch_response(scmi_info->shmem, xfer);
+ core->shmem->fetch_response(scmi_info->shmem, xfer,
+ scmi_info->io_ops->fromio);
}

static void smc_mark_txdone(struct scmi_chan_info *cinfo, int ret, diff
--git a/drivers/firmware/arm_scmi/shmem.c
b/drivers/firmware/arm_scmi/shmem.c
index 01d8a9398fe8..aded5f1cd49f 100644
--- a/drivers/firmware/arm_scmi/shmem.c
+++ b/drivers/firmware/arm_scmi/shmem.c
@@ -34,9 +34,67 @@ struct scmi_shared_mem {
u8 msg_payload[];
};

+static inline void shmem_memcpy_fromio32(void *to,
+ const volatile void __iomem
*from,
+ size_t count)
+{
+ while (count) {
+ *(u32 *)to = __raw_readl(from);
+ from += 4;
+ to += 4;
+ count -= 4;

This may not have issue, considering the 'count % 4' will be 0
and 'from' is 4 bytes aligned.

Correct, this cannot possibly happen today by virtue of msg->payload being naturally aligned on a 4 bytes boundary.

But I think it maybe better to add check if 'count' and 'from'
are not 4 bytes aligned.

Humm, what would be the fallback, or should we just WARN()?

+ }
+
+ /* Ensure all reads from I/O have completed */
+ rmb();

Is there a need to use rmb here? I am not sure, just wonder.

I personally do not think there is because there is an implicit data dependency eventually we will be consuming data that was copied into msg->payload and that will ensure that the data is there.

+}
+
+static inline void shmem_memcpy_toio32(volatile void __iomem *to,
+ const void *from,
+ size_t count)
+{
+ while (count) {
+ __raw_writel(*(u32 *)from, to);
+ from += 4;
+ to += 4;
+ count -= 4;
+ }

Ditto.

+
+ /* Ensure all writes to I/O have completed */
+ wmb();

This maybe not needed.
The mailbox will use "writel", the SMC will use "smc",
the virtio will have "hvc", both will have barrier I think.

Yes, those are all implicit barriers, I was attempting to address Christian's concerns raised in v2:

https://lore.kernel.org/all/Zr-GJts3Gu6GEkhC@pluto/
--
Florian

Next message: Qais Yousef: "[RFC PATCH 01/16] sched: cpufreq: Rename map_util_perf to sugov_apply_dvfs_headroom"
Previous message: Arnd Bergmann: "Re: [RFC} arm architecture board/feature deprecation timeline"
In reply to: Peng Fan: "RE: [PATCH v3 2/2] firmware: arm_scmi: Support 'reg-io-width' property for shared memory"
Next in thread: Peng Fan: "RE: [PATCH v3 2/2] firmware: arm_scmi: Support 'reg-io-width' property for shared memory"
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