Re: [PATCH v2] dmaengine: Create symlinks between DMA channels and slaves

From: Peter Ujfalusi
Date: Thu Jan 30 2020 - 04:42:52 EST

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Geert,

On 17/01/2020 17.30, Geert Uytterhoeven wrote:
> Currently it is not easy to find out which DMA channels are in use, and
> which slave devices are using which channels.
>
> Fix this by creating two symlinks between the DMA channel and the actual
> slave device when a channel is requested:
> 1. A "slave" symlink from DMA channel to slave device,
> 2. A "dma:<name>" symlink slave device to DMA channel.
> When the channel is released, the symlinks are removed again.
> The latter requires keeping track of the slave device and the channel
> name in the dma_chan structure.
>
> Note that this is limited to channel request functions for requesting an
> exclusive slave channel that take a device pointer (dma_request_chan()
> and dma_request_slave_channel*()).
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
> ---
> v2:
> - Add DMA_SLAVE_NAME macro,
> - Also handle channels from FIXME,
> - Add backlinks from slave device to DMA channel,
>
> On r8a7791/koelsch, the following new symlinks are created:
>
> /sys/devices/platform/soc/
> âââ e6700000.dma-controller/dma/dma0chan0/slave -> ../../../e6e20000.spi
> âââ e6700000.dma-controller/dma/dma0chan1/slave -> ../../../e6e20000.spi
> âââ e6700000.dma-controller/dma/dma0chan2/slave -> ../../../ee100000.sd
> âââ e6700000.dma-controller/dma/dma0chan3/slave -> ../../../ee100000.sd
> âââ e6700000.dma-controller/dma/dma0chan4/slave -> ../../../ee160000.sd
> âââ e6700000.dma-controller/dma/dma0chan5/slave -> ../../../ee160000.sd
> âââ e6700000.dma-controller/dma/dma0chan6/slave -> ../../../e6e68000.serial
> âââ e6700000.dma-controller/dma/dma0chan7/slave -> ../../../e6e68000.serial
> âââ e6720000.dma-controller/dma/dma1chan0/slave -> ../../../e6b10000.spi
> âââ e6720000.dma-controller/dma/dma1chan1/slave -> ../../../e6b10000.spi
> âââ e6720000.dma-controller/dma/dma1chan2/slave -> ../../../ee140000.sd
> âââ e6720000.dma-controller/dma/dma1chan3/slave -> ../../../ee140000.sd
> âââ e6b10000.spi/dma:rx -> ../e6720000.dma-controller/dma/dma1chan1
> âââ e6b10000.spi/dma:tx -> ../e6720000.dma-controller/dma/dma1chan0
> âââ e6e20000.spi/dma:rx -> ../e6700000.dma-controller/dma/dma0chan1
> âââ e6e20000.spi/dma:tx -> ../e6700000.dma-controller/dma/dma0chan0
> âââ e6e68000.serial/dma:rx -> ../e6700000.dma-controller/dma/dma0chan7
> âââ e6e68000.serial/dma:tx -> ../e6700000.dma-controller/dma/dma0chan6
> âââ ee100000.sd/dma:rx -> ../e6700000.dma-controller/dma/dma0chan3
> âââ ee100000.sd/dma:tx -> ../e6700000.dma-controller/dma/dma0chan2
> âââ ee140000.sd/dma:rx -> ../e6720000.dma-controller/dma/dma1chan3
> âââ ee140000.sd/dma:tx -> ../e6720000.dma-controller/dma/dma1chan2
> âââ ee160000.sd/dma:rx -> ../e6700000.dma-controller/dma/dma0chan5
> âââ ee160000.sd/dma:tx -> ../e6700000.dma-controller/dma/dma0chan4
>
> On r8a77951/salvator-xs:
>
> /sys/devices/platform/soc/
> âââ e6460000.dma-controller/dma/dma4chan0/slave -> ../../../e659c000.usb
> âââ e6460000.dma-controller/dma/dma4chan1/slave -> ../../../e659c000.usb
> âââ e6470000.dma-controller/dma/dma5chan0/slave -> ../../../e659c000.usb
> âââ e6470000.dma-controller/dma/dma5chan1/slave -> ../../../e659c000.usb
> âââ e6510000.i2c/dma:tx -> ../e7300000.dma-controller/dma/dma7chan0
> âââ e6550000.serial/dma:rx -> ../e7310000.dma-controller/dma/dma8chan1
> âââ e6550000.serial/dma:tx -> ../e7310000.dma-controller/dma/dma8chan0
> âââ e6590000.usb/dma:ch0 -> ../e65a0000.dma-controller/dma/dma2chan0
> âââ e6590000.usb/dma:ch1 -> ../e65a0000.dma-controller/dma/dma2chan1
> âââ e6590000.usb/dma:ch2 -> ../e65b0000.dma-controller/dma/dma3chan0
> âââ e6590000.usb/dma:ch3 -> ../e65b0000.dma-controller/dma/dma3chan1
> âââ e659c000.usb/dma:ch0 -> ../e6460000.dma-controller/dma/dma4chan0
> âââ e659c000.usb/dma:ch1 -> ../e6460000.dma-controller/dma/dma4chan1
> âââ e659c000.usb/dma:ch2 -> ../e6470000.dma-controller/dma/dma5chan0
> âââ e659c000.usb/dma:ch3 -> ../e6470000.dma-controller/dma/dma5chan1
> âââ e65a0000.dma-controller/dma/dma2chan0/slave -> ../../../e6590000.usb
> âââ e65a0000.dma-controller/dma/dma2chan1/slave -> ../../../e6590000.usb
> âââ e65b0000.dma-controller/dma/dma3chan0/slave -> ../../../e6590000.usb
> âââ e65b0000.dma-controller/dma/dma3chan1/slave -> ../../../e6590000.usb
> âââ e7300000.dma-controller/dma/dma7chan0/slave -> ../../../e6510000.i2c
> âââ e7310000.dma-controller/dma/dma8chan0/slave -> ../../../e6550000.serial
> âââ e7310000.dma-controller/dma/dma8chan1/slave -> ../../../e6550000.serial
> ---
> drivers/dma/dmaengine.c | 37 +++++++++++++++++++++++++++++++------
> include/linux/dmaengine.h | 4 ++++
> 2 files changed, 35 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 56a8420c388679d3..617c84cf6800962b 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -60,6 +60,8 @@ static long dmaengine_ref_count;
>
> /* --- sysfs implementation --- */
>
> +#define DMA_SLAVE_NAME "slave"
> +
> /**
> * dev_to_dma_chan - convert a device pointer to its sysfs container object
> * @dev - device node
> @@ -730,11 +732,11 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> if (has_acpi_companion(dev) && !chan)
> chan = acpi_dma_request_slave_chan_by_name(dev, name);
>
> - if (chan) {
> - /* Valid channel found or requester needs to be deferred */
> - if (!IS_ERR(chan) || PTR_ERR(chan) == -EPROBE_DEFER)
> - return chan;
> - }
> + if (PTR_ERR(chan) == -EPROBE_DEFER)
> + return chan;
> +
> + if (!IS_ERR_OR_NULL(chan))
> + goto found;
>
> /* Try to find the channel via the DMA filter map(s) */
> mutex_lock(&dma_list_mutex);
> @@ -754,7 +756,23 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> }
> mutex_unlock(&dma_list_mutex);
>
> - return chan ? chan : ERR_PTR(-EPROBE_DEFER);
> + if (!IS_ERR_OR_NULL(chan))
> + goto found;
> +
> + return ERR_PTR(-EPROBE_DEFER);
> +
> +found:
> + chan->slave = dev;
> + chan->name = kasprintf(GFP_KERNEL, "dma:%s", name);
> + if (!chan->name)
> + return ERR_PTR(-ENOMEM);

You will lock the channel... It is requested, but it is not released in
case of failure.

> +
> + if (sysfs_create_link(&chan->dev->device.kobj, &dev->kobj,
> + DMA_SLAVE_NAME))
> + dev_err(dev, "Cannot create DMA %s symlink\n", DMA_SLAVE_NAME);
> + if (sysfs_create_link(&dev->kobj, &chan->dev->device.kobj, chan->name))
> + dev_err(dev, "Cannot create DMA %s symlink\n", chan->name);

It is not a problem if these fail?

> + return chan;
> }
> EXPORT_SYMBOL_GPL(dma_request_chan);
>
> @@ -812,6 +830,13 @@ void dma_release_channel(struct dma_chan *chan)
> /* drop PRIVATE cap enabled by __dma_request_channel() */
> if (--chan->device->privatecnt == 0)
> dma_cap_clear(DMA_PRIVATE, chan->device->cap_mask);
> + if (chan->slave) {
> + sysfs_remove_link(&chan->slave->kobj, chan->name);
> + kfree(chan->name);
> + chan->name = NULL;
> + chan->slave = NULL;
> + }
> + sysfs_remove_link(&chan->dev->device.kobj, DMA_SLAVE_NAME);

If a non slave channel is released, then you remove the link you have
never created?

What happens if the link creation fails and here you attempt to remove
the failed ones?

> mutex_unlock(&dma_list_mutex);
> }
> EXPORT_SYMBOL_GPL(dma_release_channel);
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 2cd1d6d7ef0fcce5..2804da93e27e114b 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -238,10 +238,12 @@ struct dma_router {
> /**
> * struct dma_chan - devices supply DMA channels, clients use them
> * @device: ptr to the dma device who supplies this channel, always !%NULL
> + * @slave: ptr to the device using this channel
> * @cookie: last cookie value returned to client
> * @completed_cookie: last completed cookie for this channel
> * @chan_id: channel ID for sysfs
> * @dev: class device for sysfs
> + * @name: backlink name for sysfs
> * @device_node: used to add this to the device chan list
> * @local: per-cpu pointer to a struct dma_chan_percpu
> * @client_count: how many clients are using this channel
> @@ -252,12 +254,14 @@ struct dma_router {
> */
> struct dma_chan {
> struct dma_device *device;
> + struct device *slave;
> dma_cookie_t cookie;
> dma_cookie_t completed_cookie;
>
> /* sysfs */
> int chan_id;
> struct dma_chan_dev *dev;
> + const char *name;
>
> struct list_head device_node;
> struct dma_chan_percpu __percpu *local;
>

- PÃter

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Next message: Geert Uytterhoeven: "[PATCH] mptcp: Fix undefined mptcp_handle_ipv6_mapped for modular IPV6"
Previous message: Dan Carpenter: "Re: [PATCH v2] staging: exfat: remove 'vol_type' variable."
In reply to: Geert Uytterhoeven: "Re: [PATCH v2] dmaengine: Create symlinks between DMA channels and slaves"
Next in thread: Geert Uytterhoeven: "Re: [PATCH v2] dmaengine: Create symlinks between DMA channels and slaves"
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