Re: [PATCH 08/11] MTD: m25p80: Add option to limit SPI transfer size.

Geert Uytterhoeven
2015-06-04T06:42:59Z

On Wed, Jun 3, 2015 at 11:26 PM, Michal Suchanek <hramrach-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> 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 <hramrach-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>
> --
>
> 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-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.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
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