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[91.79.162.197]) by smtp.googlemail.com with ESMTPSA id f10sm676257ljk.95.2019.06.14.09.44.07 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 14 Jun 2019 09:44:08 -0700 (PDT) Subject: Re: [PATCH v1] dmaengine: tegra-apb: Support per-burst residue granularity To: Jon Hunter , Laxman Dewangan , Vinod Koul , Thierry Reding , Ben Dooks Cc: dmaengine@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190613210849.10382-1-digetx@gmail.com> <5fbe4374-cc9a-8212-017e-05f4dee64443@nvidia.com> <7ab96aa5-0be2-dc01-d187-eb718093eb99@nvidia.com> From: Dmitry Osipenko Message-ID: <840fcf60-8e24-ff44-a816-ef63a5f18652@gmail.com> Date: Fri, 14 Jun 2019 19:44:07 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <7ab96aa5-0be2-dc01-d187-eb718093eb99@nvidia.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org 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@codethink.co.uk/ >>> >>> Inspired-by: Ben Dooks >>> Signed-off-by: Dmitry Osipenko >>> --- >>> 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. 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?