linux-kernel - Re: [PATCH v3 1/5] dt-bindings: spi: Add SSTE support for DWC SSI controller

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Date:   Thu, 11 Nov 2021 18:06:45 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Mark Brown <broonie@...nel.org>, nandhini.srikandan@...el.com
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        robh+dt@...nel.org, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        mgross@...ux.intel.com, kris.pan@...el.com,
        kenchappa.demakkanavar@...el.com, furong.zhou@...el.com,
        mallikarjunappa.sangannavar@...el.com, mahesh.r.vaidya@...el.com,
        rashmi.a@...el.com
Subject: Re: [PATCH v3 1/5] dt-bindings: spi: Add SSTE support for DWC SSI
 controller

On Thu, Nov 11, 2021 at 03:01:12PM +0000, Mark Brown wrote:
> On Thu, Nov 11, 2021 at 05:31:08PM +0300, Serge Semin wrote:
> 
> > BTW Mark, why not to have a generic DT-property which would set that
> > flag automatically by the SPI-core subsystem seeing it's indeed a
> > client device-property? For instance there can be some property like
> > "spi-cs-toggle" DT-property which when specified for the particular
> > SPI-client DT-node will make the SPI-core subsystem to set the
> 
> Anything like this is fundamentally part of the wire protocol for the
> device, there's no need for an extra property on top of the compatible
> for the device and the driver really, really needs to know what's going
> on to avoid data corruption.  You could also use this feature together
> with varying the word size as an optimisation at runtime (eg, do long
> sequences of register writes in a single hardware operation by setting
> an appropriate word length to cause the controller to bounce chip
> select between writes).
> 
> > SPI_CS_WORD flag of the device mode? Like it has already been done for
> > "spi-cs-high"/"spi-lsb-first"/etc.
> 
> I don't think either of those properties was a good idea, there's a
> bunch of stuff in the older SPI bindings that don't make much sense.

Ok. Thanks for clarification. No new DT-property then.

Nandhini, could you please drop this patch in v4? One more time I'm sorry
for misleading you on v2.

-Sergey