linux-kernel - Re: [PATCH 2/7] spi: fsi: Fix clock running too fast

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Message-ID: <CACPK8XcJnDjt6N9KHNEG7Mhy7=mWX2OYA-Z0tfBbvHdsJC7apA@mail.gmail.com>
Date:   Tue, 25 Aug 2020 07:10:21 +0000
From:   Joel Stanley <joel@....id.au>
To:     Eddie James <eajames@...ux.ibm.com>
Cc:     Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Brad Bishop <bradleyb@...ziesquirrel.com>,
        Rob Herring <robh+dt@...nel.org>, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 2/7] spi: fsi: Fix clock running too fast

On Thu, 20 Aug 2020 at 21:06, Eddie James <eajames@...ux.ibm.com> wrote:
>
>
> On 8/20/20 12:12 PM, Mark Brown wrote:
> > On Thu, Aug 20, 2020 at 12:02:23PM -0500, Eddie James wrote:
> >> From: Brad Bishop <bradleyb@...ziesquirrel.com>
> >>
> >> Use a clock divider tuned to a 200MHz FSI clock.  Use of the previous
> >> divider at 200MHz results in corrupt data from endpoint devices. Ideally
> >> the clock divider would be calculated from the FSI clock, but that
> >> would require some significant work on the FSI driver.
> > Presumably this divider was chosen for FSI clocks that aren't 200MHz -
> > how will those be handled?
>
>
> They aren't handled at the moment, but 200MHz FSI represents the worst
> case, as it's the maximum. Slower FSI clocks will simply result in
> slower SPI clocks.

That would be a good addition to the commit message, as I had the same
question too.

Cheers,

Joel