Date:   Fri, 2 Oct 2020 23:08:29 +0300
From:   Serge Semin <Sergey.Semin@...kalelectronics.ru>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
CC:     Serge Semin <fancer.lancer@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Alexey Malahov <Alexey.Malahov@...kalelectronics.ru>,
        Ramil Zaripov <Ramil.Zaripov@...kalelectronics.ru>,
        Pavel Parkhomenko <Pavel.Parkhomenko@...kalelectronics.ru>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        "wuxu . wu" <wuxu.wu@...wei.com>, Feng Tang <feng.tang@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 02/21] spi: dw: Add DWC SSI capability

On Fri, Oct 02, 2020 at 10:46:09PM +0300, Serge Semin wrote:
> On Fri, Oct 02, 2020 at 09:26:07PM +0300, Andy Shevchenko wrote:
> > On Fri, Oct 2, 2020 at 8:18 PM Serge Semin
> > <Sergey.Semin@...kalelectronics.ru> wrote:
> > >
> > > On Fri, Oct 02, 2020 at 01:19:29PM +0300, Andy Shevchenko wrote:
> > > > On Fri, Oct 02, 2020 at 01:28:10AM +0300, Serge Semin wrote:
> > > > > Currently DWC SSI core is supported by means of setting up the
> > > > > core-specific update_cr0() callback. It isn't suitable for multiple
> > > > > reasons. First of all having exported several methods doing the same thing
> > > > > but for different chips makes the code harder to maintain. Secondly the
> > > > > spi-dw-core driver exports the methods, then the spi-dw-mmio driver sets
> > > > > the private data callback with one of them so to be called by the core
> > > > > driver again. That makes the code logic too complicated. Thirdly using
> > > > > callbacks for just updating the CR0 register is problematic, since in case
> > > > > if the register needed to be updated from different parts of the code,
> > > > > we'd have to create another callback (for instance the SPI device-specific
> > > > > parameters don't need to be calculated each time the SPI transfer is
> > > > > submitted, so it's better to pre-calculate the CR0 data at the SPI-device
> > > > > setup stage).
> > > > >
> > > > > So keeping all the above in mind let's discard the update_cr0() callbacks,
> > > > > define a generic and static dw_spi_update_cr0() method and create the
> > > > > DW_SPI_CAP_DWC_SSI capability, which when enabled would activate the
> > > > > alternative CR0 register layout.
> > > > >
> > > > > While at it add the comments to the code path of the normal DW APB SSI
> > > > > controller setup to make the dw_spi_update_cr0() method looking coherent.
> > > >
> > >
> > > > What the point to increase indentation level and produce additional churn?
> > > > Can't you simply leave functions, unexport them, and call in one conditional of
> > > > whatever new function is called?
> > >
> > > I forgot to mention that in the commit log, there is another reason why it's
> > > better to create a generic dw_spi_update_cr0() instead of doing what you suggest.
> > > As it will be seen from the following up patches, the dw_spi_update_cr0() function
> > > (to be more precise it's successor, but anyway) will be used from the SPI memory
> > > ops implementation. So if-else-ing here and there isn't a good idea for
> > > maintainability. For the same reason of the maintainability it's better to have a
> > > generic method which reflects all the config peculiarities, so in case of any
> > > changes they would be not be forgotten to be introduced for both DWC SSI and DW
> > > APB SSI parts of the setup procedures. As I see it that overbeats the additional
> > > indentation level drawback.
> > 
> 
> > What I meant is to leave functions as is and call them under conditional
> > 
> > if ()
> >  call one
> > else
> >  call another
> 
> Yeah, I understood what you meant. What you suggest would be a better solution
> if I needed to call the dw_spi_update_cr0() method just from a single place of
> the driver (but in that case I wouldn't need to replace the callback-based
> approach with the Capabilities-based one at all). The thing is that the
> dw_spi_update_cr0() will be also called from the SPI memory exec_op() callback
> (see patch "[PATCH v3 17/21] spi: dw: Add memory operations support" and the
> method dw_spi_update_config() invocation) in the same way as it is called from
> the SPI core transfer-one callback. Following your suggestion I would have to
> implement the same "if () call one else call another" pattern there too. Copying
> it here and there would be a weak design from the maintainability point of view
> and from the coding style too. Much better is to create a generic
> dw_spi_update_cr0() (later in this patchset it will be renamed to
> dw_spi_update_config()...), which would work for both DWC SSI and DW APB SSI by
> embedding the "if (is_CAP) call one else call another" into the method itself as
> I suggested in this patch.

Oh, and the same "if-else" pattern would need to be either left in the
dw_spi_get_cr0()/dw_spi_prepare_cr0() or added around the dw_spi_prepare_cr0()
method invocation with creating two versions of it. So no, I'd stick with the
design I suggested in this patch: just two "if-else"s and the generic versions
of the dw_spi_prepare_cr0() and dw_spi_update_cr0() functions.

-Sergey

> 
> -Sergey
> 
> > 
> > 
> > -- 
> > With Best Regards,
> > Andy Shevchenko

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