On 02/07/2019 15:41, Dmitry Osipenko wrote: > 02.07.2019 16:41, Jon Hunter пишет: >> >> On 02/07/2019 14:22, Dmitry Osipenko wrote: >>> 02.07.2019 15:54, Jon Hunter пишет: >>>> >>>> On 02/07/2019 12:37, Dmitry Osipenko wrote: >>>>> 02.07.2019 14:20, Jon Hunter пишет: >>>>>> >>>>>> On 27/06/2019 20:47, 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 chromium web browser. The patch is >>>>>>> based on the original work that was made by Ben Dooks and a patch from >>>>>>> downstream kernel. It was tested on Tegra20 and Tegra30 devices. >>>>>>> >>>>>>> Link: https://lore.kernel.org/lkml/20190424162348.23692-1-ben.dooks@xxxxxxxxxxxxxxx/ >>>>>>> Link: https://nv-tegra.nvidia.com/gitweb/?p=linux-4.4.git;a=commit;h=c7bba40c6846fbf3eaad35c4472dcc7d8bbc02e5 >>>>>>> Inspired-by: Ben Dooks <ben.dooks@xxxxxxxxxxxxxxx> >>>>>>> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx> >>>>>>> --- >>>>>>> >>>>>>> Changelog: >>>>>>> >>>>>>> v3: Added workaround for a hardware design shortcoming that results >>>>>>> in a words counter wraparound before end-of-transfer bit is set >>>>>>> in a cyclic mode. >>>>>>> >>>>>>> v2: Addressed review comments made by Jon Hunter to v1. We won't try >>>>>>> to get words count if dma_desc is on free list as it will result >>>>>>> in a NULL dereference because this case wasn't handled properly. >>>>>>> >>>>>>> The residual value is now updated properly, avoiding potential >>>>>>> integer overflow by adding the "bytes" to the "bytes_transferred" >>>>>>> instead of the subtraction. >>>>>>> >>>>>>> drivers/dma/tegra20-apb-dma.c | 69 +++++++++++++++++++++++++++++++---- >>>>>>> 1 file changed, 62 insertions(+), 7 deletions(-) >>>>>>> >>>>>>> diff --git a/drivers/dma/tegra20-apb-dma.c b/drivers/dma/tegra20-apb-dma.c >>>>>>> index 79e9593815f1..71473eda28ee 100644 >>>>>>> --- a/drivers/dma/tegra20-apb-dma.c >>>>>>> +++ b/drivers/dma/tegra20-apb-dma.c >>>>>>> @@ -152,6 +152,7 @@ struct tegra_dma_sg_req { >>>>>>> bool last_sg; >>>>>>> struct list_head node; >>>>>>> struct tegra_dma_desc *dma_desc; >>>>>>> + unsigned int words_xferred; >>>>>>> }; >>>>>>> >>>>>>> /* >>>>>>> @@ -496,6 +497,7 @@ static void tegra_dma_configure_for_next(struct tegra_dma_channel *tdc, >>>>>>> tdc_write(tdc, TEGRA_APBDMA_CHAN_CSR, >>>>>>> nsg_req->ch_regs.csr | TEGRA_APBDMA_CSR_ENB); >>>>>>> nsg_req->configured = true; >>>>>>> + nsg_req->words_xferred = 0; >>>>>>> >>>>>>> tegra_dma_resume(tdc); >>>>>>> } >>>>>>> @@ -511,6 +513,7 @@ static void tdc_start_head_req(struct tegra_dma_channel *tdc) >>>>>>> typeof(*sg_req), node); >>>>>>> tegra_dma_start(tdc, sg_req); >>>>>>> sg_req->configured = true; >>>>>>> + sg_req->words_xferred = 0; >>>>>>> tdc->busy = true; >>>>>>> } >>>>>>> >>>>>>> @@ -797,6 +800,61 @@ static int tegra_dma_terminate_all(struct dma_chan *dc) >>>>>>> return 0; >>>>>>> } >>>>>>> >>>>>>> +static unsigned int tegra_dma_sg_bytes_xferred(struct tegra_dma_channel *tdc, >>>>>>> + struct tegra_dma_sg_req *sg_req) >>>>>>> +{ >>>>>>> + unsigned long status, wcount = 0; >>>>>>> + >>>>>>> + if (!list_is_first(&sg_req->node, &tdc->pending_sg_req)) >>>>>>> + return 0; >>>>>>> + >>>>>>> + 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 sg_req->req_len; >>>>>>> + >>>>>>> + wcount = get_current_xferred_count(tdc, sg_req, wcount); >>>>>>> + >>>>>>> + if (!wcount) { >>>>>>> + /* >>>>>>> + * If wcount wasn't ever polled for this SG before, then >>>>>>> + * simply assume that transfer hasn't started yet. >>>>>>> + * >>>>>>> + * Otherwise it's the end of the transfer. >>>>>>> + * >>>>>>> + * The alternative would be to poll the status register >>>>>>> + * until EOC bit is set or wcount goes UP. That's so >>>>>>> + * because EOC bit is getting set only after the last >>>>>>> + * burst's completion and counter is less than the actual >>>>>>> + * transfer size by 4 bytes. The counter value wraps around >>>>>>> + * in a cyclic mode before EOC is set(!), so we can't easily >>>>>>> + * distinguish start of transfer from its end. >>>>>>> + */ >>>>>>> + if (sg_req->words_xferred) >>>>>>> + wcount = sg_req->req_len - 4; >>>>>>> + >>>>>>> + } else if (wcount < sg_req->words_xferred) { >>>>>>> + /* >>>>>>> + * This case shall not ever happen because EOC bit >>>>>>> + * must be set once next cyclic transfer is started. >>>>>> >>>>>> I am not sure I follow this and why this condition cannot happen for >>>>>> cyclic transfers. What about non-cyclic transfers? >>>>> >>>>> It cannot happen because the EOC bit will be set in that case. The counter wraps >>>>> around when the transfer of a last burst happens, EOC bit is guaranteed to be set >>>>> after completion of the last burst. That's my observation after a thorough testing, >>>>> it will be very odd if EOC setting happened completely asynchronously. >>>> >>>> I see how you know that the EOC is set. Anyway, you check if the EOC is >>>> set before and if so return sg_req->req_len prior to this test. >>>> >>>> Maybe I am missing something, but what happens if we are mid block when >>>> dmaengine_tx_status() is called? That happen asynchronously right? >>> >>> >>> Do you mean asynchronously in regards to the ISR? Or something else? >> >> In the sense that the client can call dmaengine_tx_status() at anytime >> to check the status of a transfer. > > Should be alright, I think this patch covers all of possible cases: > > 1) Start of transfer, when wcount=0. > 2) Middle of transfer, when wcount!=0. > 3) End of transfer, when wcount=0. > 4) End of transfer, when wcount!=0 and EOC is set. I think I see my problem I read 'wcount < sg_req->req_len' and NOT 'wcount < sg_req->words_xferred'. So yes this should be fine. Jon -- nvpublic
