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

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Date:   Wed, 17 Nov 2021 11:59:29 +0000
From:   "Srikandan, Nandhini" <nandhini.srikandan@...el.com>
To:     Serge Semin <fancer.lancer@...il.com>,
        Mark Brown <broonie@...nel.org>
CC:     Serge Semin <Sergey.Semin@...kalelectronics.ru>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "mgross@...ux.intel.com" <mgross@...ux.intel.com>,
        "Pan, Kris" <kris.pan@...el.com>,
        "Demakkanavar, Kenchappa" <kenchappa.demakkanavar@...el.com>,
        "Zhou, Furong" <furong.zhou@...el.com>,
        "Sangannavar, Mallikarjunappa" 
        <mallikarjunappa.sangannavar@...el.com>,
        "Vaidya, Mahesh R" <mahesh.r.vaidya@...el.com>,
        "A, Rashmi" <rashmi.a@...el.com>
Subject: RE: [PATCH v3 3/5] spi: dw: Add support for master mode selection for
 DWC SSI controller



> -----Original Message-----
> From: Serge Semin <fancer.lancer@...il.com>
> Sent: Wednesday, November 17, 2021 12:46 AM
> To: Mark Brown <broonie@...nel.org>; Srikandan, Nandhini
> <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; Pan, Kris
> <kris.pan@...el.com>; Demakkanavar, Kenchappa
> <kenchappa.demakkanavar@...el.com>; Zhou, Furong
> <furong.zhou@...el.com>; Sangannavar, Mallikarjunappa
> <mallikarjunappa.sangannavar@...el.com>; Vaidya, Mahesh R
> <mahesh.r.vaidya@...el.com>; A, Rashmi <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 04:25:02PM +0000, Mark Brown wrote:
> > On Thu, Nov 11, 2021 at 07:06:27PM +0300, Serge Semin wrote:
> > > On Thu, Nov 11, 2021 at 03:14:26PM +0000, Mark Brown wrote:
> >
> > > > 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.
> >
> > > In that case the corresponding platform code would have needed to
> > > have that peculiarity properly handled and not to use a generic
> > > compatibles like "snps,dwc-ssi-1.01a" or "snps,dw-apb-ssi", which
> > > are supposed to be utilized for the default IP-core configs only.
> > > For the sake of the code simplification I'd stick to setting that
> > > flag for each generic DWC SSI-compatible device. That will be also
> > > helpful for DWC SSIs which for some reason have the slave-mode
> enabled by default.
> >
> 
> > That's easier right up until the point where it explodes - I'd prefer
> > to be more conservative here.  Fixing things up after the fact gets
> > painful when people end up only finding the bug in released kernels,
> > especially if it's distro end users or similar rather than developers.
> 
> Since IP-core and components versions is now supported that will easy to
> implement. Thanks for merging the corresponding series in BTW.
> 
> >
> > > Alternatively the driver could read the IP-core version from the
> > > DW_SPI_VERSION register, parse it (since it's in ASCII) and then use
> > > it in the conditional Master mode activation here. But that could
> > > have been a better solution in case if the older IP-cores would have
> > > used that bit for something special, while Nandhini claims it was
> reserved.
> > > So in this case I would stick with a simpler approach until we get
> > > to face any problem in this matter, especially seeing we already
> > > pocking the reserved bits of the CTRL0 register in this driver in
> > > the
> > > spi_hw_init() method when it comes to the DFS field width detection.
> >
> > If the device has a version register checking that seems ideal - the
> > infrastructure will most likely be useful in future anyway.  A bit of
> > a shame that it's an ASCII string though.
> 
> That's what the patchset has been implemented for in the first place
> https://lore.kernel.org/linux-spi/20211115181917.7521-1-
> Sergey.Semin@...kalelectronics.ru/
> 
> Nandhini, Mark has just merged in the series that adds the IP-core versions
> infrastructure support to the DW SSI driver.  So now you can easily convert
> this patch to be using that new interface like this:
> -               if (dws->caps & DW_SPI_CAP_KEEMBAY_MST)
> -                       cr0 |= DWC_SSI_CTRLR0_KEEMBAY_MST;
> +               /* CTRLR0[31] MST */
> +		if (dw_spi_ver_is_ge(dws, HSSI, 102A))
> +       	        cr0 |= DWC_HSSI_CTRLR0_MST;
> 
> Please don't forget to convert the DWC_SSI_CTRLR0_KEEMBAY_MST name to
> something like DWC_HSSI_CTRLR0_MST and place it at the top of the DWC
> HSSI CTRLR0 register macros list.
> 
> -Sergey
Sure, I will test this patch set on our hardware and then use the IP-core version infrastructure support 
and make the changes as mentioned for MST bit.

- Nandhini