On 14/06/2019 17:44, Dmitry Osipenko wrote: > 14.06.2019 18:24, Jon Hunter пишет: >> >> On 14/06/2019 16:21, Jon Hunter wrote: >>> >>> On 13/06/2019 22:08, Dmitry Osipenko wrote: >>>> Tegra's APB DMA engine updates words counter after each transferred burst >>>> of data, hence it can report transfer's residual with more fidelity which >>>> may be required in cases like audio playback. In particular this fixes >>>> audio stuttering during playback in a chromiuim web browser. The patch is >>>> based on the original work that was made by Ben Dooks [1]. It was tested >>>> on Tegra20 and Tegra30 devices. >>>> >>>> [1] https://lore.kernel.org/lkml/20190424162348.23692-1-ben.dooks@xxxxxxxxxxxxxxx/ >>>> >>>> Inspired-by: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx> >>>> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx> >>>> --- >>>> drivers/dma/tegra20-apb-dma.c | 35 ++++++++++++++++++++++++++++------- >>>> 1 file changed, 28 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c >>>> index 79e9593815f1..c5af8f703548 100644 >>>> --- a/drivers/dma/tegra20-apb-dma.c >>>> +++ b/drivers/dma/tegra20-apb-dma.c >>>> @@ -797,12 +797,36 @@ static int tegra_dma_terminate_all(struct dma_chan *dc) >>>> return 0; >>>> } >>>> >>>> +static unsigned int tegra_dma_update_residual(struct tegra_dma_channel *tdc, >>>> + struct tegra_dma_sg_req *sg_req, >>>> + struct tegra_dma_desc *dma_desc, >>>> + unsigned int residual) >>>> +{ >>>> + unsigned long status, wcount = 0; >>>> + >>>> + if (!list_is_first(&sg_req->node, &tdc->pending_sg_req)) >>>> + return residual; >>>> + >>>> + if (tdc->tdma->chip_data->support_separate_wcount_reg) >>>> + wcount = tdc_read(tdc, TEGRA_APBDMA_CHAN_WORD_TRANSFER); >>>> + >>>> + status = tdc_read(tdc, TEGRA_APBDMA_CHAN_STATUS); >>>> + >>>> + if (!tdc->tdma->chip_data->support_separate_wcount_reg) >>>> + wcount = status; >>>> + >>>> + if (status & TEGRA_APBDMA_STATUS_ISE_EOC) >>>> + return residual - sg_req->req_len; >>>> + >>>> + return residual - get_current_xferred_count(tdc, sg_req, wcount); >>>> +} >>>> + >>>> static enum dma_status tegra_dma_tx_status(struct dma_chan *dc, >>>> dma_cookie_t cookie, struct dma_tx_state *txstate) >>>> { >>>> struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc); >>>> + struct tegra_dma_sg_req *sg_req = NULL; >>>> struct tegra_dma_desc *dma_desc; >>>> - struct tegra_dma_sg_req *sg_req; >>>> enum dma_status ret; >>>> unsigned long flags; >>>> unsigned int residual; >>>> @@ -838,6 +862,8 @@ static enum dma_status tegra_dma_tx_status(struct dma_chan *dc, >>>> residual = dma_desc->bytes_requested - >>>> (dma_desc->bytes_transferred % >>>> dma_desc->bytes_requested); >>>> + residual = tegra_dma_update_residual(tdc, sg_req, dma_desc, >>>> + residual); >>> >>> I had a quick look at this, I am not sure that we want to call >>> tegra_dma_update_residual() here for cases where the dma_desc is on the >>> free_dma_desc list. In fact, couldn't this be simplified a bit for case >>> where the dma_desc is on the free list? In that case I believe that the >>> residual should always be 0. >> >> Actually, no, it could be non-zero in the case the transfer is aborted. > > Looks like everything should be fine as-is. I am still not sure we want to call this for the case where dma_desc is on the free list. > BTW, it's a bit hard to believe that there is any real benefit from the > free_dma_desc list at all, maybe worth to just remove it? I think you need to elaborate a bit more here. I am not a massive fan of this driver, but I am also not in the mood for changing unless there is a good reason. Cheers Jon -- nvpublic
