Re: [PATCH 2/2] spi: Add Baikal-T1 System Boot SPI Controller driver

From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Mark Brown <broonie@kernel.org>,
	Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Paul Burton <paulburton@kernel.org>,
	Ralf Baechle <ralf@linux-mips.org>,
	Lee Jones <lee.jones@linaro.org>,
	Miquel Raynal <miquel.raynal@bootlin.com>,
	Arnd Bergmann <arnd@arndb.de>, Rob Herring <robh+dt@kernel.org>,
	<linux-mips@vger.kernel.org>,
	devicetree <devicetree@vger.kernel.org>,
	John Garry <john.garry@huawei.com>,
	Chuanhong Guo <gch981213@gmail.com>,
	Eddie James <eajames@linux.ibm.com>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Chris Packham <chris.packham@alliedtelesis.co.nz>,
	Tomer Maimon <tmaimon77@gmail.com>,
	Masahisa Kojima <masahisa.kojima@linaro.org>,
	Krzysztof Kozlowski <krzk@kernel.org>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Jassi Brar <jaswinder.singh@linaro.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-spi <linux-spi@vger.kernel.org>
Subject: Re: [PATCH 2/2] spi: Add Baikal-T1 System Boot SPI Controller driver
Date: Fri, 8 May 2020 19:24:55 +0300	[thread overview]
Message-ID: <20200508162455.3cgfquqmbx7ep2zf@mobilestation> (raw)
In-Reply-To: <CAHp75VcaVGHfYN1hjD5eKgpKJkpKEif8NxBGO1YF61_apv82Kg@mail.gmail.com>

On Fri, May 08, 2020 at 01:26:52PM +0300, Andy Shevchenko wrote:
> On Fri, May 8, 2020 at 1:15 PM Serge Semin
> <Sergey.Semin@baikalelectronics.ru> wrote:
> >
> > On Fri, May 08, 2020 at 01:03:11PM +0300, Andy Shevchenko wrote:
> > > On Fri, May 8, 2020 at 12:37 PM Serge Semin
> > > <Sergey.Semin@baikalelectronics.ru> wrote:
> > > >
> > > > This SPI-controller is a part of the Baikal-T1 System Controller and
> > > > is based on the DW APB SSI IP-core, but with very limited resources:
> > > > no IRQ, no DMA, only a single native chip-select and just 8 bytes Tx/Rx
> > > > FIFO available. In order to provide a transparent initial boot code
> > > > execution this controller is also utilized by an vendor-specific block,
> > > > which provides an CS0 SPI flash direct mapping interface. Since both
> > > > direct mapping and SPI controller normal utilization are mutual exclusive
> > > > only a one of these interfaces can be used to access an external SPI
> > > > slave device. Taking into account the peculiarities of the controller
> > > > registers and physically mapped SPI flash access, very limited resources
> > > > and seeing the normal usecase of the controller is to access an external
> > > > SPI-nor flash, we decided to create a dedicated SPI driver for it.
> > >
> > > It seems a lot of code.
> > > Why can't you use spi-dw-mmio.c et al.?
> >
> > I said above why. Even though the registers set is similar It's too specific
> > to be integrated into the generic DW SSI driver.
> 
> At least you may do at the beginning is to reuse header spi-dw.h and
> put your stuff under
> spi-dw-baikal.c or so. Then, look at the spi-dw.c and check what can
> be reused (I think a lot).

Nah, It's not a lot, barely a few things. What is useful is the registers map
(though it has to be shifted and most of the registers are unused), IO operations
(two small read-write methods with questionable design) and possibly a few lines
of config setting procedure.

You think I didn't had in mind to integrate this controller support into
the generic driver or resuse something from there? If it was worth a try I would
have done it.

-Sergey

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