| Message ID | 1430137404-30236-1-git-send-email-jonathanh@nvidia.com |
|---|---|
| State | Superseded, archived |
| Headers | show |
diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c index 0e035a8cf401..03b0e22b4a68 100644 --- a/drivers/dma/dmaengine.c +++ b/drivers/dma/dmaengine.c @@ -571,11 +571,16 @@ struct dma_chan *dma_get_any_slave_channel(struct dma_device *device) chan = private_candidate(&mask, device, NULL, NULL); if (chan) { + dma_cap_set(DMA_PRIVATE, device->cap_mask); + device->privatecnt++; err = dma_chan_get(chan); if (err) { pr_debug("%s: failed to get %s: (%d)\n", __func__, dma_chan_name(chan), err); chan = NULL; + + if (--device->privatecnt == 0) + dma_cap_clear(DMA_PRIVATE, device->cap_mask); } }
The function dma_get_any_slave_channel() allocates private DMA channels by calling the internal private_candidate() function. However, when doing so, if a channel is successfully allocated, neither the DMA_PRIVATE flag is set or the privatecnt variable is incremented for the DMA controller. This will cause the following problems ... 1. A DMA controller initialised with the DMA_PRIVATE flag set (ie. channels should always be private) will become public incorrectly when a channel is allocated and then released. This is because: - A DMA controller initialised with DMA_PRIVATE set will have a initial privatecnt of 1. - The privatecnt is not incremented by dma_get_any_slave_channel(). - When the channel is released via dma_release_channel(), the privatecnt is decremented and the DMA_PRIVATE flag is cleared because the privatecnt value is 0. 2. For a DMA controller initialised with the DMA_PRIVATE flag set, if more than one DMA channel is allocated successfully via dma_get_any_slave_channel() and then one channel is released, the following issues can occur: i). All channels currently allocated will appear as public because the DMA_PRIVATE will be cleared (as described in #1). ii). Subsequent calls to dma_get_any_slave_channel() will fail even if there are channels available. The reason this fails is that the private_candidate() function (called by dma_get_any_slave_channel()) will detect the DMA controller is not private but has active channels and so cannot allocate any private channels (see below code snippet). /* devices with multiple channels need special handling as we need to * ensure that all channels are either private or public. */ if (dev->chancnt > 1 && !dma_has_cap(DMA_PRIVATE, dev->cap_mask)) list_for_each_entry(chan, &dev->channels, device_node) { /* some channels are already publicly allocated */ if (chan->client_count) return NULL; } 3. For a DMA controller initialised with the DMA_PRIVATE flag unset, if a private channel is allocated via dma_get_any_slave_channel(), then the DMA controller will still appear as public because the DMA_PRIVATE flag is not set and this will cause: i). The allocated channel to appear as public ii). Prevent any further private channels being allocated via dma_get_any_slave_channel() (because private_candidate() will fail in the same way as described in 2.ii above). Fix this by incrementing the privatecnt in dma_get_any_slave_channel(). If dma_get_any_slave_channel() allocates a channel also ensure the DMA_PRIVATE flag is set, in case it was not before. If the privatecnt becomes 0 then the DMA_PRIVATE flag should be cleared. Cc: Stephen Warren <swarren@nvidia.com> Signed-off-by: Jon Hunter <jonathanh@nvidia.com> --- This issue was found when attempting to open and close a serial interface, that uses DMA, multiple times on a tegra device. When opening the serial device a 2nd time after closing, the DMA channel allocation would fail. drivers/dma/dmaengine.c | 5 +++++ 1 file changed, 5 insertions(+)