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

[Jagan Teki]

On Fri, Nov 23, 2018 at 6:24 PM Simon Goldschmidt
<sgoldschmidt at de.pepperl-fuchs.com> wrote:
>
> [Responding from my work address due to problems with gmail]
>
> On 23.11.2018 13:27, Jagan Teki wrote:
> > 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.
>
> That's not completely true. Adding "jedec,spi-nor" to U-Boot would
> definitively make it less likely to run into this issue.

I don't this is what we discussed above, adding the Linux compatible
with relevant spi-frequnecy make the issue non-reproducible this is
what exactly we ended-up.


>
> However, Linux works correctly without "jedec,spi-nor", so people can
> still run into problems when porting a dts from Linux. This is why I
> still would like to get this in.

Why? do they specify property?