From: Mark Brown <broonie@kernel.org>
To: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Vignesh R <vigneshr@ti.com>,
Frode Isaksen <fisaksen@baylibre.com>,
Cyrille Pitchen <cyrille.pitchen@atmel.com>,
Richard Weinberger <richard@nod.at>,
David Woodhouse <dwmw2@infradead.org>,
Brian Norris <computersforpeace@gmail.com>,
Marek Vasut <marek.vasut@gmail.com>,
linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org,
linux-omap@vger.kernel.org, linux-spi@vger.kernel.org
Subject: Re: [RFC PATCH 2/2] mtd: devices: m25p80: Enable spi-nor bounce buffer support
Date: Thu, 2 Mar 2017 17:00:41 +0000 [thread overview]
Message-ID: <20170302170041.hfix33mhzgqydmvh@sirena.org.uk> (raw)
In-Reply-To: <20170302152921.1c031b57@bbrezillon>
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On Thu, Mar 02, 2017 at 03:29:21PM +0100, Boris Brezillon wrote:
> Vignesh R <vigneshr@ti.com> wrote:
> > Or SPI core can be extended in a way similar to this RFC. That is, SPI
> > master driver will set a flag to request SPI core to use of bounce
> > buffer for vmalloc'd buffers. And spi_map_buf() just uses bounce buffer
> > in case buf does not belong to kmalloc region based on the flag.
> That's a better approach IMHO. Note that the decision should not only
I don't understand how the driver is supposed to tell if it might need a
bounce buffer due to where the memory is allocated and the caches used
by the particular system it is used on? The suggestion to pass via
scatterlists seems a bit more likely to work but even then I'm not clear
that drivers doing PIO would play well.
> be based on the buffer type, but also on the transfer length and/or
> whether the controller supports transferring non physically contiguous
> buffers.
The reason most drivers only look at the transfer length when deciding
that they can DMA is that most controllers are paired with DMA
controllers that are sensibly implemented, the only factor they're
selecting on is the copybreak for performance.
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WARNING: multiple messages have this Message-ID (diff)
From: Mark Brown <broonie@kernel.org>
To: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Frode Isaksen <fisaksen@baylibre.com>,
linux-omap@vger.kernel.org, Vignesh R <vigneshr@ti.com>,
Richard Weinberger <richard@nod.at>,
linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org,
Marek Vasut <marek.vasut@gmail.com>,
linux-mtd@lists.infradead.org,
Cyrille Pitchen <cyrille.pitchen@atmel.com>,
Brian Norris <computersforpeace@gmail.com>,
David Woodhouse <dwmw2@infradead.org>
Subject: Re: [RFC PATCH 2/2] mtd: devices: m25p80: Enable spi-nor bounce buffer support
Date: Thu, 2 Mar 2017 17:00:41 +0000 [thread overview]
Message-ID: <20170302170041.hfix33mhzgqydmvh@sirena.org.uk> (raw)
In-Reply-To: <20170302152921.1c031b57@bbrezillon>
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On Thu, Mar 02, 2017 at 03:29:21PM +0100, Boris Brezillon wrote:
> Vignesh R <vigneshr@ti.com> wrote:
> > Or SPI core can be extended in a way similar to this RFC. That is, SPI
> > master driver will set a flag to request SPI core to use of bounce
> > buffer for vmalloc'd buffers. And spi_map_buf() just uses bounce buffer
> > in case buf does not belong to kmalloc region based on the flag.
> That's a better approach IMHO. Note that the decision should not only
I don't understand how the driver is supposed to tell if it might need a
bounce buffer due to where the memory is allocated and the caches used
by the particular system it is used on? The suggestion to pass via
scatterlists seems a bit more likely to work but even then I'm not clear
that drivers doing PIO would play well.
> be based on the buffer type, but also on the transfer length and/or
> whether the controller supports transferring non physically contiguous
> buffers.
The reason most drivers only look at the transfer length when deciding
that they can DMA is that most controllers are paired with DMA
controllers that are sensibly implemented, the only factor they're
selecting on is the copybreak for performance.
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next prev parent reply other threads:[~2017-03-02 18:18 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-27 12:08 [RFC PATCH 0/2] mtd: spi-nor: Handle vmalloc'd buffers Vignesh R
2017-02-27 12:08 ` Vignesh R
2017-02-27 12:08 ` [RFC PATCH 1/2] mtd: spi-nor: Introduce bounce buffer to handle " Vignesh R
2017-02-27 12:08 ` Vignesh R
2017-02-28 21:39 ` Richard Weinberger
2017-02-28 21:39 ` Richard Weinberger
2017-03-01 5:13 ` Vignesh R
2017-03-01 5:13 ` Vignesh R
2017-03-01 10:09 ` Cyrille Pitchen
2017-03-01 10:09 ` Cyrille Pitchen
2017-03-01 10:18 ` Boris Brezillon
2017-03-01 10:18 ` Boris Brezillon
2017-03-01 11:18 ` Frode Isaksen
2017-03-01 11:18 ` Frode Isaksen
2017-03-01 12:12 ` Boris Brezillon
2017-03-01 12:12 ` Boris Brezillon
2017-03-01 11:50 ` Vignesh R
2017-03-01 11:50 ` Vignesh R
2017-02-27 12:08 ` [RFC PATCH 2/2] mtd: devices: m25p80: Enable spi-nor bounce buffer support Vignesh R
2017-02-27 12:08 ` Vignesh R
2017-02-28 21:41 ` Richard Weinberger
2017-03-01 4:54 ` Vignesh R
2017-03-01 4:54 ` Vignesh R
2017-03-01 10:43 ` Cyrille Pitchen
2017-03-01 10:43 ` Cyrille Pitchen
2017-03-01 11:14 ` Frode Isaksen
2017-03-01 11:14 ` Frode Isaksen
2017-03-01 11:46 ` Vignesh R
2017-03-01 11:46 ` Vignesh R
2017-03-01 11:46 ` Vignesh R
2017-03-01 12:23 ` Boris Brezillon
2017-03-01 12:23 ` Boris Brezillon
2017-03-01 14:21 ` Cyrille Pitchen
2017-03-01 14:21 ` Cyrille Pitchen
2017-03-01 14:28 ` Boris Brezillon
2017-03-01 14:28 ` Boris Brezillon
2017-03-01 14:28 ` Boris Brezillon
2017-03-01 14:30 ` Cyrille Pitchen
2017-03-01 14:30 ` Cyrille Pitchen
2017-03-01 14:30 ` Cyrille Pitchen
2017-03-01 15:52 ` Mark Brown
2017-03-01 16:04 ` Boris Brezillon
2017-03-01 16:04 ` Boris Brezillon
2017-03-01 16:55 ` Boris Brezillon
2017-03-01 16:55 ` Boris Brezillon
2017-03-02 9:06 ` Frode Isaksen
2017-03-02 9:06 ` Frode Isaksen
2017-03-02 13:54 ` Vignesh R
2017-03-02 13:54 ` Vignesh R
2017-03-02 14:29 ` Boris Brezillon
2017-03-02 14:29 ` Boris Brezillon
2017-03-02 15:03 ` Frode Isaksen
2017-03-02 15:03 ` Frode Isaksen
2017-03-02 15:25 ` Boris Brezillon
2017-03-02 15:25 ` Boris Brezillon
2017-03-03 9:02 ` Frode Isaksen
2017-03-03 9:02 ` Frode Isaksen
2017-03-02 16:45 ` Cyrille Pitchen
2017-03-02 16:45 ` Cyrille Pitchen
2017-03-02 17:00 ` Mark Brown [this message]
2017-03-02 17:00 ` Mark Brown
2017-03-02 19:49 ` Boris Brezillon
2017-03-02 19:49 ` Boris Brezillon
2017-03-03 12:50 ` Mark Brown
2017-03-03 12:50 ` Mark Brown
2017-03-06 11:47 ` Vignesh R
2017-03-06 11:47 ` Vignesh R
2017-03-14 13:21 ` Vignesh R
2017-02-27 14:03 ` [RFC PATCH 0/2] mtd: spi-nor: Handle vmalloc'd buffers Frode Isaksen
2017-02-27 14:03 ` Frode Isaksen
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