| Message ID | 1439816935-27554-1-git-send-email-geert+renesas@glider.be (mailing list archive) |
|---|---|
| State | Accepted |
| Delegated to: | Geert Uytterhoeven |
| Headers | show |
On Mon, Aug 17, 2015 at 03:08:55PM +0200, Geert Uytterhoeven wrote: > dma_request_slave_channel_compat() is meant for drivers that support > both DT and legacy platform device based probing: if DT channel DMA > setup fails, it will fall back to platform data based DMA channel setup, > using hardcoded DMA channel IDs and a filter function. > > However, if the DTS doesn't provide a "dmas" property for the device, > the fallback is also used. If the legacy filter function is not > hardcoded in the DMA slave driver, but comes from platform data, it will > be NULL. Then dma_request_slave_channel_compat() will succeed > incorrectly, and return a DMA channel, as a NULL legacy filter function > actually means "all channels are OK", not "do not match". > > Later, when trying to use that DMA channel, it will fail with: > > rcar-dmac e6700000.dma-controller: rcar_dmac_prep_slave_sg: bad parameter: len=1, id=-22 > > To fix this, ensure that both the filter function and the DMA channel ID > are not NULL before using the legacy fallback. > > Note that some DMA slave drivers can handle this failure, and will fall > back to PIO. > > See also commit 056f6c87028544de ("dmaengine: shdma: Make dummy > shdma_chan_filter() always return false"), which fixed the same issue > for the case where shdma_chan_filter() is hardcoded in a DMA slave > driver. Applied, thanks
diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h index bdae84ab305bca59..6a22cf1b63c24ffb 100644 --- a/include/linux/dmaengine.h +++ b/include/linux/dmaengine.h @@ -1197,6 +1197,9 @@ static inline struct dma_chan if (chan) return chan; + if (!fn || !fn_param) + return NULL; + return __dma_request_channel(mask, fn, fn_param); } #endif /* DMAENGINE_H */
dma_request_slave_channel_compat() is meant for drivers that support both DT and legacy platform device based probing: if DT channel DMA setup fails, it will fall back to platform data based DMA channel setup, using hardcoded DMA channel IDs and a filter function. However, if the DTS doesn't provide a "dmas" property for the device, the fallback is also used. If the legacy filter function is not hardcoded in the DMA slave driver, but comes from platform data, it will be NULL. Then dma_request_slave_channel_compat() will succeed incorrectly, and return a DMA channel, as a NULL legacy filter function actually means "all channels are OK", not "do not match". Later, when trying to use that DMA channel, it will fail with: rcar-dmac e6700000.dma-controller: rcar_dmac_prep_slave_sg: bad parameter: len=1, id=-22 To fix this, ensure that both the filter function and the DMA channel ID are not NULL before using the legacy fallback. Note that some DMA slave drivers can handle this failure, and will fall back to PIO. See also commit 056f6c87028544de ("dmaengine: shdma: Make dummy shdma_chan_filter() always return false"), which fixed the same issue for the case where shdma_chan_filter() is hardcoded in a DMA slave driver. Suggested-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> --- include/linux/dmaengine.h | 3 +++ 1 file changed, 3 insertions(+)