From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Serge Semin <fancer.lancer@gmail.com>,
Vinod Koul <vkoul@kernel.org>, Viresh Kumar <vireshk@kernel.org>,
Dan Williams <dan.j.williams@intel.com>,
Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
Arnd Bergmann <arnd@arndb.de>, Rob Herring <robh+dt@kernel.org>,
<linux-mips@vger.kernel.org>, <devicetree@vger.kernel.org>,
<dmaengine@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 10/10] dmaengine: dw: Initialize max_sg_nents with nollp flag
Date: Thu, 28 May 2020 18:50:17 +0300 [thread overview]
Message-ID: <20200528155017.ayetroojyvxl74kb@mobilestation> (raw)
In-Reply-To: <20200528145630.GV1634618@smile.fi.intel.com>
On Thu, May 28, 2020 at 05:56:30PM +0300, Andy Shevchenko wrote:
> On Wed, May 27, 2020 at 01:50:21AM +0300, Serge Semin wrote:
> > Multi-block support provides a way to map the kernel-specific SG-table so
> > the DW DMA device would handle it as a whole instead of handling the
> > SG-list items or so called LLP block items one by one. So if true LLP
> > list isn't supported by the DW DMA engine, then soft-LLP mode will be
> > utilized to load and execute each LLP-block one by one. The soft-LLP mode
> > of the DMA transactions execution might not work well for some DMA
> > consumers like SPI due to its Tx and Rx buffers inter-dependency. Let's
> > expose the nollp flag indicating the soft-LLP mode by means of the
> > max_sg_nents capability, so the DMA consumer would be ready to somehow
> > workaround errors caused by such mode being utilized.
> >
>
> In principal I agree, one nit below.
> If you are okay with it, feel free to add my Rb tag.
>
> > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
> > Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > Cc: Rob Herring <robh+dt@kernel.org>
> > Cc: linux-mips@vger.kernel.org
> > Cc: devicetree@vger.kernel.org
> >
> > ---
> >
> > Changelog v3:
> > - This is a new patch created as a result of the discussion with Vinud and
> > Andy in the framework of DW DMA burst and LLP capabilities.
> > ---
> > drivers/dma/dw/core.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
> > index 29c4ef08311d..b850eb7fd084 100644
> > --- a/drivers/dma/dw/core.c
> > +++ b/drivers/dma/dw/core.c
> > @@ -1054,6 +1054,15 @@ static void dwc_caps(struct dma_chan *chan, struct dma_slave_caps *caps)
> > struct dw_dma_chan *dwc = to_dw_dma_chan(chan);
> >
> > caps->max_burst = dwc->max_burst;
> > +
> > + /*
> > + * It might be crucial for some devices to have the hardware
> > + * accelerated multi-block transfers supported, aka LLPs in DW DMAC
> > + * notation. So if LLPs are supported then max_sg_nents is set to
> > + * zero which means unlimited number of SG entries can be handled in a
> > + * single DMA transaction, otherwise it's just one SG entry.
> > + */
>
> > + caps->max_sg_nents = dwc->nollp;
>
> To be on the safer side I would explicitly do it like
>
> if (dwc->nollp)
> /* your nice comment */
> = 1;
> else
> /* Unlimited */
> = 0;
>
> type or content of nollp theoretically can be changed and this will affect maximum segments.
Agree. Though I don't like formatting you suggested. If I add my nice comment
between if-statement and assignment the the former will be look detached from
the if-statement, which seems a bit ugly. So I'd leave the comment above the
whole if-else statement, especially seeing I've already mentioned there about
the unlimited number of SG entries there.
/*
* It might be crucial for some devices to have the hardware
* accelerated multi-block transfers supported, aka LLPs in DW DMAC
* notation. So if LLPs are supported then max_sg_nents is set to
* zero which means unlimited number of SG entries can be handled in a
* single DMA transaction, otherwise it's just one SG entry.
*/
if (dwc->nollp)
caps->max_sg_nents = 1;
else
caps->max_sg_nents = 0;
-Sergey
>
> > }
> >
> > int do_dma_probe(struct dw_dma_chip *chip)
> > --
> > 2.26.2
> >
>
> --
> With Best Regards,
> Andy Shevchenko
>
>
next prev parent reply other threads:[~2020-05-28 15:50 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-26 22:50 [PATCH v3 00/10] dmaengine: dw: Take Baikal-T1 SoC DW DMAC peculiarities into account Serge Semin
2020-05-26 22:50 ` [PATCH v3 01/10] dt-bindings: dma: dw: Convert DW DMAC to DT binding Serge Semin
2020-05-26 22:50 ` [PATCH v3 02/10] dt-bindings: dma: dw: Add max burst transaction length property Serge Semin
2020-05-26 22:50 ` [PATCH v3 03/10] dmaengine: Introduce min burst length capability Serge Semin
2020-05-28 14:21 ` Andy Shevchenko
2020-05-26 22:50 ` [PATCH v3 04/10] dmaengine: Introduce max SG list entries capability Serge Semin
2020-05-28 14:22 ` Andy Shevchenko
2020-05-26 22:50 ` [PATCH v3 05/10] dmaengine: Introduce DMA-device device_caps callback Serge Semin
2020-05-28 14:42 ` Andy Shevchenko
2020-05-28 15:19 ` Serge Semin
2020-05-28 20:34 ` Andy Shevchenko
2020-05-26 22:50 ` [PATCH v3 06/10] dmaengine: dw: Take HC_LLP flag into account for noLLP auto-config Serge Semin
2020-05-26 22:50 ` [PATCH v3 07/10] dmaengine: dw: Set DMA device max segment size parameter Serge Semin
2020-05-26 22:50 ` [PATCH v3 08/10] dmaengine: dw: Add dummy device_caps callback Serge Semin
2020-05-28 14:53 ` Andy Shevchenko
2020-05-28 15:27 ` Serge Semin
2020-05-28 20:29 ` Andy Shevchenko
2020-05-28 20:34 ` Serge Semin
2020-05-26 22:50 ` [PATCH v3 09/10] dmaengine: dw: Introduce max burst length hw config Serge Semin
2020-05-28 14:52 ` Andy Shevchenko
2020-05-28 15:40 ` Serge Semin
2020-05-28 19:53 ` Serge Semin
2020-05-28 20:38 ` Andy Shevchenko
2020-05-26 22:50 ` [PATCH v3 10/10] dmaengine: dw: Initialize max_sg_nents with nollp flag Serge Semin
2020-05-28 14:56 ` Andy Shevchenko
2020-05-28 15:50 ` Serge Semin [this message]
2020-05-28 20:31 ` Andy Shevchenko
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=20200528155017.ayetroojyvxl74kb@mobilestation \
--to=sergey.semin@baikalelectronics.ru \
--cc=Alexey.Malahov@baikalelectronics.ru \
--cc=andriy.shevchenko@linux.intel.com \
--cc=arnd@arndb.de \
--cc=dan.j.williams@intel.com \
--cc=devicetree@vger.kernel.org \
--cc=dmaengine@vger.kernel.org \
--cc=fancer.lancer@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mips@vger.kernel.org \
--cc=robh+dt@kernel.org \
--cc=tsbogend@alpha.franken.de \
--cc=vireshk@kernel.org \
--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).