From: Dmitry Osipenko <digetx@gmail.com>
To: Jon Hunter <jonathanh@nvidia.com>,
Laxman Dewangan <ldewangan@nvidia.com>,
Vinod Koul <vkoul@kernel.org>,
Thierry Reding <thierry.reding@gmail.com>,
Ben Dooks <ben.dooks@codethink.co.uk>
Cc: dmaengine@vger.kernel.org, linux-tegra@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] dmaengine: tegra-apb: Support per-burst residue granularity
Date: Fri, 14 Jun 2019 19:44:07 +0300 [thread overview]
Message-ID: <840fcf60-8e24-ff44-a816-ef63a5f18652@gmail.com> (raw)
In-Reply-To: <7ab96aa5-0be2-dc01-d187-eb718093eb99@nvidia.com>
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 <ben.dooks@codethink.co.uk>
>>> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
>>> ---
>>> 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?
next prev parent reply other threads:[~2019-06-14 16:44 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-13 21:08 [PATCH v1] dmaengine: tegra-apb: Support per-burst residue granularity Dmitry Osipenko
2019-06-14 15:21 ` Jon Hunter
2019-06-14 15:24 ` Jon Hunter
2019-06-14 16:44 ` Dmitry Osipenko [this message]
2019-06-17 10:57 ` Jon Hunter
2019-06-17 12:41 ` Dmitry Osipenko
2019-06-18 8:47 ` Jon Hunter
2019-06-18 9:45 ` Dmitry Osipenko
2019-06-18 22:22 ` Ben Dooks
2019-06-18 23:27 ` Dmitry Osipenko
2019-06-19 10:04 ` Jon Hunter
2019-06-19 10:08 ` Ben Dooks
2019-06-19 10:13 ` Jon Hunter
2019-06-19 10:16 ` Ben Dooks
2019-06-19 10:27 ` Dmitry Osipenko
2019-06-19 10:55 ` Jon Hunter
2019-06-19 11:10 ` Dmitry Osipenko
2019-06-19 12:22 ` Jon Hunter
2019-06-19 13:52 ` Dmitry Osipenko
2019-06-19 21:56 ` Dmitry Osipenko
2019-06-19 12:55 ` Ben Dooks
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=840fcf60-8e24-ff44-a816-ef63a5f18652@gmail.com \
--to=digetx@gmail.com \
--cc=ben.dooks@codethink.co.uk \
--cc=dmaengine@vger.kernel.org \
--cc=jonathanh@nvidia.com \
--cc=ldewangan@nvidia.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-tegra@vger.kernel.org \
--cc=thierry.reding@gmail.com \
--cc=vkoul@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).