Messages in this thread | | | Subject | Re: [PATCH v2] dmaengine: Create symlinks between DMA channels and slaves | From | Peter Ujfalusi <> | Date | Thu, 30 Jan 2020 12:22:37 +0200 |
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Hi Geert,
On 30/01/2020 11.51, Geert Uytterhoeven wrote: > Hi Peter, > > On Thu, Jan 30, 2020 at 10:42 AM Peter Ujfalusi <peter.ujfalusi@ti.com> wrote: >> 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@glider.be> > >>> --- 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. > > True. Perhaps this error should just be ignored, cfr. below. > However, if this operation fails, chances are high the system will die very soon > anyway.
Yeah, I'll fix it up in a series I'm preparing.
> >>> + >>> + 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? > > IMHO, a failure to create these links is not fatal for the operation of > the device, and thus can be ignored. Just like for debugfs.
OK, then these should not be dev_err, but dev_warn. I'll include this is also in a fixup patch.
> >>> + 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? > > sysfs_remove_link() should handle removing non-existent links, and just > return -ENOENT.
True, just followed the call chain and tested as well, but the DMA_SLAVE_NAME symlink should be also removed within the if (chan->slave) {} block as it is never created for non slave channels.
Also including inn my fixup patch.
> > Gr{oetje,eeting}s, > > Geert >
- Péter
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