linux-kernel - Re: [PATCH v3 3/5] spi: dw: Add support for master mode selection for DWC SSI controller

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Date:   Thu, 11 Nov 2021 15:14:26 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        nandhini.srikandan@...el.com, 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 3/5] spi: dw: Add support for master mode selection
 for DWC SSI controller

On Thu, Nov 11, 2021 at 05:52:46PM +0300, Serge Semin wrote:
> On Thu, Nov 11, 2021 at 02:16:05PM +0000, Mark Brown wrote:
> > On Thu, Nov 11, 2021 at 02:51:59PM +0800, nandhini.srikandan@...el.com wrote:

> > > Add support to select the controller mode as master mode by setting
> > > Bit 31 of CTRLR0 register. This feature is supported for controller
> > > versions above v1.02.

> > Clearly older versions of the controller can also run in this mode...

> Yes, but the driver doesn't support the slave mode at the moment.
> So always enabling the master mode seems natural. (see my next comment
> also concerning this matter)

The commit message makes it sound like master mode is only supported for
the newer versions.

> > This makes the configuration unconditional, it's not gated by controller
> > version checks or any kind of quirk any more meaning that if anything

> We have already discussed this feature in v2:
> https://patchwork.kernel.org/project/spi-devel-general/patch/20210824085856.12714-3-nandhini.srikandan@intel.com/
> Since that bit has been reserved before 1.02a but is no available for
> any DWC SSI controller and the driver doesn't support the SPI-slave mode
> at the moment I suggested to just always set that flag for the DWC SSI
> code. Please see my reply to Nandhini here:

Given that people seem to frequently customise these IPs when
integrating them I wouldn't trust people not to have added some other
control into that reserved bit doing some magic stuff that's useful in
their system.

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