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?
> 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 <e...@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
> return ret;
>
> spin_lock_irqsave(&c->vc.lock, flags);
> vd = vchan_find_desc(&c->vc, cookie);
> if (vd) {
> - txstate->residue =
> - bcm2835_dma_desc_size(to_bcm2835_dma_desc(&vd->tx));
> + residue = bcm2835_dma_desc_size(to_bcm2835_dma_desc(&vd->tx));
> } else if (c->desc && c->desc->vd.tx.cookie == cookie) {
> struct bcm2835_desc *d = c->desc;
> dma_addr_t pos;
> @@ -591,11 +591,25 @@ static enum dma_status bcm2835_dma_tx_status(struct
> dma_chan *chan,
> else
> pos = 0;
>
> - txstate->residue = bcm2835_dma_desc_size_pos(d, pos);
> + residue = bcm2835_dma_desc_size_pos(d, pos);
> +
> + /*
> + * If our non-cyclic transfer is done, then report
> + * complete and trigger the next tx now. This lets
> + * the dmaengine API be used synchronously from an IRQ
> + * handler.
> + */
> + if (!d->cyclic && residue == 0) {
> + vchan_cookie_complete(&c->desc->vd);
> + bcm2835_dma_start_desc(c);
> + ret = dma_cookie_status(chan, cookie, txstate);
> + }
> } else {
> - txstate->residue = 0;
> + residue = 0;
> }
>
> + dma_set_residue(txstate, residue);
> +
> spin_unlock_irqrestore(&c->vc.lock, flags);
>
> return ret;
> --
> 2.8.0.rc3
>
--
~Vinod
