From: arnd@arndb•de (Arnd Bergmann)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v6] spi: orion.c: Add direct access mode
Date: Mon, 02 May 2016 09:28:34 +0200 [thread overview]
Message-ID: <8919835.yGyvx4h0Tr@wuerfel> (raw)
In-Reply-To: <5726F7F3.9070700@denx.de>
On Monday 02 May 2016 08:47:15 Stefan Roese wrote:
> On 20.04.2016 12:11, Stefan Roese wrote:
> > This patch adds support for the direct write mode to the Orion SPI
> > driver which is used on the Marvell Armada based SoCs. In this direct
> > mode, all data written to (or read from) a specifically mapped MBus
> > window (linked to one SPI chip-select on one of the SPI controllers)
> > will be transferred directly to the SPI bus. Without the need to control
> > the SPI registers in between. This can improve the SPI transfer rate in
> > such cases.
> >
> > Currently only the direct write mode is supported. This mode especially
> > benefits from the SPI direct mode, as the data bytes are written
> > head-to-head to the SPI bus, without any additional addresses, that
> > are also written in the direct read mode.
> >
> > One use-case for this direct write mode is, programming a FPGA bitstream
> > image into the FPGA connected to the SPI bus at maximum speed.
> >
> > This mode is described in chapter "22.5.2 Direct Write to SPI" in the
> > Marvell Armada XP Functional Spec Datasheet.
> >
> > It should be possible to support SPI-NOR and SPI-NAND devices via
> > this direct access mode as well. But this needs further work, e.g.:
> > - The mapping of the MBus window needs to get extended to span
> > the complete flash device size
> > - The address / control data needs to get inserted into the SPI
> > controller registers
> >
> > Signed-off-by: Stefan Roese <sr@denx•de>
> > Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons•com>
> > Cc: Gregory CLEMENT <gregory.clement@free-electrons•com>
> > Cc: Andrew Lunn <andrew@lunn•ch>
> > Cc: Arnd Bergmann <arnd@arndb•de>
> > Cc: Mark Brown <broonie@kernel•org>
>
> Its been a while since v6 of this direct write access mode has been
> posted. This is a gentle ping on its status.
>
> Arnd / Mark, do you have any additional change requests or are you okay
> with the current version?
No objections, please add
Acked-by: Arnd Bergmann <arnd@arndb•de>
Two questions though:
- you now always send a multiple of four byte in each transfer, are
there any downsides in doing this, e.g. some SPI devices that might
get confused by receiving additional uninitialized data?
- How does the performance compare to the normal mode, is it basically
unchanged, or does this patch make things faster?
Arnd
next prev parent reply other threads:[~2016-05-02 7:28 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-20 10:11 [PATCH v6] spi: orion.c: Add direct access mode Stefan Roese
2016-04-20 11:58 ` Gregory CLEMENT
2016-04-20 12:09 ` Stefan Roese
2016-06-16 9:23 ` Gregory CLEMENT
2016-06-16 9:42 ` Stefan Roese
2016-05-02 6:47 ` Stefan Roese
2016-05-02 7:28 ` Arnd Bergmann [this message]
2016-05-02 10:33 ` Stefan Roese
2016-05-02 15:40 ` Mark Brown
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