linux-kernel - Re: [PATCH v2 4/4] soc: samsung: exynos-chipid: convert to driver and merge exynos-asv

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Date:   Tue, 8 Dec 2020 09:47:49 +0100
From:   'Krzysztof Kozlowski' <krzk@...nel.org>
To:     Pankaj Dubey <pankaj.dubey@...sung.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        'Sylwester Nawrocki' <snawrocki@...nel.org>,
        'Marek Szyprowski' <m.szyprowski@...sung.com>,
        'Bartlomiej Zolnierkiewicz' <b.zolnierkie@...sung.com>,
        'Arnd Bergmann' <arnd@...db.de>,
        'Chanwoo Choi' <cw00.choi@...sung.com>,
        'Alim Akhtar' <alim.akhtar@...sung.com>
Subject: Re: [PATCH v2 4/4] soc: samsung: exynos-chipid: convert to driver
 and merge exynos-asv

On Tue, Dec 08, 2020 at 12:31:23PM +0530, Pankaj Dubey wrote:
> 
> 
> > -----Original Message-----
> > From: Krzysztof Kozlowski <krzk@...nel.org>
> > Sent: Tuesday, December 8, 2020 12:35 AM
> > To: Krzysztof Kozlowski <krzk@...nel.org>; linux-arm-
> > kernel@...ts.infradead.org; linux-samsung-soc@...r.kernel.org; linux-
> > kernel@...r.kernel.org
> > Cc: Sylwester Nawrocki <snawrocki@...nel.org>; Marek Szyprowski
> > <m.szyprowski@...sung.com>; Bartlomiej Zolnierkiewicz
> > <b.zolnierkie@...sung.com>; Arnd Bergmann <arnd@...db.de>; Chanwoo
> > Choi <cw00.choi@...sung.com>; Alim Akhtar <alim.akhtar@...sung.com>;
> > Pankaj Dubey <pankaj.dubey@...sung.com>
> > Subject: [PATCH v2 4/4] soc: samsung: exynos-chipid: convert to driver and
> > merge exynos-asv
> > 
> > The Exynos Chip ID driver on Exynos SoCs has so far only informational
> > purpose - to expose the SoC device in sysfs.  No other drivers depend on
> it
> > so there is really no benefit of initializing it early.
> > 
> 
> One of the intention behind initializing Exynos Chip ID driver in early
> stage was to simplify code in arch/arm/mach-exynos specifically calls such
> as soc_is_exynosXXXX. 
> But there were lot of resistance from community to add any such calls (or
> exported function) from mach-exynos files to the driver file. Whereas some
> other SoC code is using the same, e.g. tegra_get_chip_id being called from
> mach-tegra files to drivers/soc/tegra/. Unfortunately we could not accept
> similar solution for Exynos SoC and hence could not get rid of
> soc_is_exynosxXXX and similar macros from various file in mach-exynos and
> eventually converting those files into a full-fledged driver files. 
> 
> Any opinion how can we achieve this if we convert Exynos Chip ID driver to a
> regular driver?

a. Some parts of mach code can be moved to drivers and then use OF calls.

b. The ones which cannot be moved, could use soc_device_match() assuming
   they are called after the soc-bus is operational - so after
   core_initcalls.

c. The ones which are called early or without cache coherency
   (soc_device_match() uses krefs()), cannot be converted.

This chip ID conversion indeed kills case (b) above... which I am not
sure is worth bothering. Which parts of code could be moved like this?
Not mentioning that none of this work have happened since few years...

Best regards,
Krzysztof