Messages in this thread | | | Date | Tue, 03 Dec 2013 10:50:05 -0700 | From | Stephen Warren <> | Subject | Re: [PATCH V4] dma: add channel request API that supports deferred probe |
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On 11/26/2013 10:04 AM, Stephen Warren wrote: > From: Stephen Warren <swarren@nvidia.com> > > dma_request_slave_channel() simply returns NULL whenever DMA channel > lookup fails. Lookup could fail for two distinct reasons: > > a) No DMA specification exists for the channel name. > This includes situations where no DMA specifications exist at all, or > other general lookup problems. > > b) A DMA specification does exist, yet the driver for that channel is not > yet registered. > > Case (b) should trigger deferred probe in client drivers. However, since > they have no way to differentiate the two situations, it cannot. > > Implement new function dma_request_slave_channel_reason(), which performs > identically to dma_request_slave_channel(), except that it returns an > error-pointer rather than NULL, which allows callers to detect when > deferred probe should occur. > > Eventually, all drivers should be converted to this new API, the old API > removed, and the new API renamed to the more desirable name. This patch > doesn't convert the existing API and all drivers in one go, since some > drivers call dma_request_slave_channel() then dma_request_channel() if > that fails. That would require either modifying dma_request_channel() in > the same way, or adding extra error-handling code to all affected > drivers, and there are close to 100 drivers using the other API, rather > than just the 15-20 or so that use dma_request_slave_channel(), which > might be tenable in a single patch. > > acpi_dma_request_slave_chan_by_name() doesn't currently implement > deferred probe. It should, but this will be addressed later. > > Acked-by: Dan Williams <dan.j.williams@intel.com> > Signed-off-by: Stephen Warren <swarren@nvidia.com> > --- > v4: > * Add {} around both branches in of_dma_request_slave_channel(). > v3: > * s/_or_err/_reason/ in the new API name. > * Simplify changes to of_dma_request_slave_channel() so that the new > "bool defer" parameter is not needed. > * Revert changes to acpi-dma.c and handle the return value conversion > in dma_request_slave_channel_reason() instead. > * Mention that acpi_dma_request_slave_chan_by_name() should implement > deferred probe, but that will happen later. > v2: > * include <linux/err.h> in <linux/dmaengine.h> > * Return -ENODATA if slave_id or chan_id out-of-range. > * Return an error-pointer not NULL if we can't find a matching DMA > controller or translate the channel. > > This patch is a dependency for: > * A series that reworks many of the Tegra drivers. > * A series that enhances ASoC's dmaengine code to support deferred probe. > > As such, it needs to go into a topic branch on its own, based directly > on 3.13-rc1. If the DMA maintainers ack the patches I'm happy to create > this topic branch myself and send a pull request to the DMA tree. Or the > patches can be applied to a topic branch by the DMA maintainers and I > will merge their topic branch into the Tegra rework branch that I > mentioned.
Vinod, does this patch look OK to you? Are you able to stage it into a topic branch that I can pull into the Tegra tree as a dependency?
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