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

[Simon Glass]

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>