[U-Boot] [PATCH v2] dm: spi: prevent setting a speed of 0 Hz

[Jagan Teki]

On Fri, Nov 23, 2018 at 1:51 AM <sjg at google.com> wrote:
>
> On Fri, 16 Nov 2018 at 12:40, Simon Goldschmidt
> <simon.k.r.goldschmidt at gmail.com> wrote:
> >
> > On 31.10.2018 07:42, Simon Goldschmidt wrote:
> > > On Wed, Oct 31, 2018 at 7:22 AM Jagan Teki <jagan at amarulasolutions.com> wrote:
> > >> On Wed, Oct 31, 2018 at 1:40 AM Simon Goldschmidt
> > >> <simon.k.r.goldschmidt at gmail.com> wrote:
> > >>> When the device tree is missing a correct spi slave description below
> > >>> the bus (compatible "spi-flash" or spi-max-frequency are missing),
> > >>> the 'set_speed' callback can be called with 'speed' == 0 Hz.
> > >>> At least with cadence qspi, this leads to a division by zero.
> > >>>
> > >>> Prevent this by initializing speed to 100 kHz in this case (same
> > >>> fallback value as is done in 'dm_spi_claim_bus') and issue a warning
> > >>> to console.
> > >> Why can't driver plat->frequency in cadence driver initialize 100KH?
> > >> plat->frequency = fdtdec_get_int(blob, node, "spi-max-frequency", 100000)
> > > I'm not sure I understand.
> > > The cadence driver initializes its 'plat->max_hz' from
> > > "spi-max-frequency" property and defaults to 500 kHz. No problem
> > > there.
> > >
> > > However, the problem I want to solve is if someone puts a flash chip
> > > below there which has compatible != "spi-flash", they will get a hard
> > > fault which is hard to debug. This is because the node is not parsed
> > > because of the wrong compatible string (even if there is an
> > > "spi-max-frequency" property) and thus, "sf probe" tries to continue
> > > with 0 Hz.
> > >
> > > And this can happen easily when porting device trees from Linux as
> > > there, the boards have compatible "n25q00" etc. instead of
> > > "spi-flash", which is U-Boot specific (sadly).
> > >
> > > This patch is not required to make valid U-Boot devicetrees work, it
> > > is meant to get better error handling for devicetrees ported from
> > > Linux.
> > >
> > > An even better fix would be for U-Boot not to require the compatible =
> > > "spi-flash" string but just work correctly with Linux device trees,
> > > but that's not within my possibilities right now :-(
> >
> > Ping? This is a bug that should hit nearly everyone porting a board dts
> > working in Linux to U-Boot, can we please have some kind of fix for this?
> > Currently, using a dts with an spi flash chip that works in Linux may
> > abort in U-Boot...
>
> Reviewed-by: Simon Glass <sjg at chromium.org>
>
> Applied to u-boot-dm/master, thanks!

I hold this because, there is a discussion going on with me and
Simon.k about Linux compatible "jedec,spi-nor".  adding support for
this binding would eventually not reproduce this issue.