From mboxrd@z Thu Jan 1 00:00:00 1970 From: geert@linux-m68k.org (Geert Uytterhoeven) Date: Thu, 4 Jun 2015 08:42:59 +0200 Subject: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size. In-Reply-To: <8fc4b9f5291a509c4c35782a1337bf536f1019af.1433364398.git.hramrach@gmail.com> References: <8fc4b9f5291a509c4c35782a1337bf536f1019af.1433364398.git.hramrach@gmail.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Jun 3, 2015 at 11:26 PM, Michal Suchanek wrote: > On sunxi the SPI controller currently does not have DMA support and fails > any transfer larger than 63 bytes. This is a driver limitation, not a hardware limitation. > On Exynos the pl330 DMA controller fails any transfer larger than 64kb > when using slower speed like 40MHz and any transfer larger than 128bytes > when running at 133MHz. This may be a driver bug. > The best thing is that in both cases the controller can just lock up and > never finish potentially leaving the hardware in unusable state. > > So it is required that the m25p80 driver actively prevents doing > transfers that are too large for the current driver state on a > particular piece of hardware. OK. > Signed-off-by: Michal Suchanek > > -- > > Update commit message and documentation text. > --- > .../devicetree/bindings/mtd/jedec,spi-nor.txt | 6 ++++++ > drivers/mtd/devices/m25p80.c | 24 ++++++++++++++++++++-- > 2 files changed, 28 insertions(+), 2 deletions(-) > > diff --git a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt > index 2bee681..4e63ae8 100644 > --- a/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt > +++ b/Documentation/devicetree/bindings/mtd/jedec,spi-nor.txt > @@ -19,6 +19,12 @@ Optional properties: > all chips and support for it can not be detected at runtime. > Refer to your chips' datasheet to check if this is supported > by your chip. > +- linux,max_tx_len : With some SPI controller drivers possible transfer size is > + limited. This may be hardware or driver bug. > + Transfer data in chunks no larger than this value. > + Using this option may severely degrade performance and > + possibly flash memory life when max_tx_len is smaller than > + flash page size (typically 256 bytes) DT describes the hardware, not buggy drivers. So IMHO this doesn't belong in DT, but it can be a field in struct spi_master. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds