From: Andy Shevchenko <andriy.shevchenko@intel.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: linux-arm-kernel@lists.infradead.org,
"Sam Ravnborg" <sam@ravnborg.org>,
"Mark Brown" <broonie@kernel.org>,
"Haojian Zhuang" <haojian.zhuang@gmail.com>,
linux-spi@vger.kernel.org, "Noralf Trønnes" <noralf@tronnes.org>,
"DRI Development" <dri-devel@lists.freedesktop.org>,
"Robert Jarzmik" <robert.jarzmik@free.fr>,
"Daniel Mack" <daniel@zonque.org>
Subject: Re: [PATCH] spi: pxa2xx: Set controller->max_transfer_size in dma mode
Date: Mon, 21 Oct 2019 14:08:57 +0300 [thread overview]
Message-ID: <20191021110857.GR32742@smile.fi.intel.com> (raw)
In-Reply-To: <20191017070638.GB32742@smile.fi.intel.com>
On Thu, Oct 17, 2019 at 10:06:38AM +0300, Andy Shevchenko wrote:
> On Thu, Oct 17, 2019 at 08:44:26AM +0200, Daniel Vetter wrote:
> > In DMA mode we have a maximum transfer size, past that the driver
> > falls back to PIO (see the check at the top of pxa2xx_spi_transfer_one).
> > Falling back to PIO for big transfers defeats the point of a dma engine,
> > hence set the max transfer size to inform spi clients that they need
> > to do something smarter.
> >
> > This was uncovered by the drm_mipi_dbi spi panel code, which does
> > large spi transfers, but stopped splitting them after:
> >
> > commit e143364b4c1774f68e923a5a0bb0fca28ac25888
> > Author: Noralf Trønnes <noralf@tronnes.org>
> > Date: Fri Jul 19 17:59:10 2019 +0200
> >
> > drm/tinydrm: Remove tinydrm_spi_max_transfer_size()
> >
> > After this commit the code relied on the spi core to split transfers
> > into max dma-able blocks, which also papered over the PIO fallback issue.
> >
> > Fix this by setting the overall max transfer size to the DMA limit,
> > but only when the controller runs in DMA mode.
> >
>
> Thank you, Daniel!
Mark, can be this applied?
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2019-10-21 11:08 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-16 19:57 [PATCH] spi: pxa2xx: Set controller->max_transfer_size in dma mode Daniel Vetter
2019-10-16 21:30 ` Noralf Trønnes
2019-10-16 21:49 ` Mark Brown
2019-10-17 6:44 ` Daniel Vetter
2019-10-17 7:06 ` Andy Shevchenko
2019-10-21 11:08 ` Andy Shevchenko [this message]
2019-10-21 11:35 ` Mark Brown
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