[PATCH] dmaengine: bcm2835: Fix polling for completion of DMA with interrupts masked.
eric at anholt.net
Mon Jun 6 23:10:38 PDT 2016
Vinod Koul <vinod.koul at intel.com> writes:
> On Mon, Jun 06, 2016 at 10:33:18AM -0700, Eric Anholt wrote:
>> Vinod Koul <vinod.koul at intel.com> writes:
>> > On Fri, Jun 03, 2016 at 07:29:11PM -0700, Eric Anholt wrote:
>> >> The tx_status hook is supposed to be safe to call from interrupt
>> >> context, but it wouldn't ever return completion for the last transfer,
>> >> meaning you couldn't poll for DMA completion with interrupts masked.
>> > and why is that?
>> Maybe this was poorly worded. How about:
>> The tx_status hook is supposed to be safe to call from interrupt
>> context. However, the current transfer currently only gets marked
>> complete by the IRQ handler, so if interrupts were masked then polling
>> for completion would never finish.
> Sound better :)
>> >> This fixes IRQ handling for bcm2835's DSI1, which requires using the
>> >> DMA engine to write its registers due to a bug in the AXI bridge.
>> >> Signed-off-by: Eric Anholt <eric at anholt.net>
>> >> ---
>> >> drivers/dma/bcm2835-dma.c | 24 +++++++++++++++++++-----
>> >> 1 file changed, 19 insertions(+), 5 deletions(-)
>> >> diff --git a/drivers/dma/bcm2835-dma.c b/drivers/dma/bcm2835-dma.c
>> >> index 6149b27c33ad..320461c578e3 100644
>> >> --- a/drivers/dma/bcm2835-dma.c
>> >> +++ b/drivers/dma/bcm2835-dma.c
>> >> @@ -570,16 +570,16 @@ static enum dma_status bcm2835_dma_tx_status(struct dma_chan *chan,
>> >> struct virt_dma_desc *vd;
>> >> enum dma_status ret;
>> >> unsigned long flags;
>> >> + u32 residue;
>> >> ret = dma_cookie_status(chan, cookie, txstate);
>> >> - if (ret == DMA_COMPLETE || !txstate)
>> >> + if (ret == DMA_COMPLETE)
>> > Why do you change this? txstate can be NULL, so no point calculating reside
>> > for those cases
>> The point was to go into the "Calculate where we're at in our current
>> DMA (if the current DMA is the one we're asking about status for)" path,
>> so that we could note when the DMA is complete even when there's no
>> txstate passed in.
> Can you explain what you mean by current DMA!
> The claulation is always done for 'descriptor' represnted by the cookie. So
> it doesnt not matter...!
By current I mean the current descriptor that has been submitted to the
hardware, in bcm2835_chan->desc.
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