linux-kernel - Re: [PATCH v3 2/9] soc: samsung: Convert exynos-chipid driver to use the regmap API

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Date:   Wed, 21 Aug 2019 15:10:53 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Sylwester Nawrocki <s.nawrocki@...sung.com>
Cc:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Sylwester Nawrocki <snawrocki@...nel.org>,
        Jon Hunter <jonathanh@...dia.com>, robh+dt@...nel.org,
        vireshk@...nel.org, devicetree@...r.kernel.org, kgene@...nel.org,
        pankaj.dubey@...sung.com,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-pm@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v3 2/9] soc: samsung: Convert exynos-chipid driver to use
 the regmap API

On Wed, 21 Aug 2019 at 14:41, Sylwester Nawrocki <s.nawrocki@...sung.com> wrote:
>
> On 8/21/19 14:16, Krzysztof Kozlowski wrote:
> >>> I'm also inclined to have it converted to a regular driver.  We already
> >>> have "exynos-asv" driver matching on the chipid node (patch 3/9).
> >>> The ASV patches will not be merged soon anyway, all this needs some more
> >>> thought. Krzysztof, can we abandon the chipid patches for now? Your
> >>
> >> chipid driver is good and useful on its own. The preferred solution
> >> IMHO would be to just revert "soc: samsung: Convert exynos-chipid
> >> driver to use the regmap API" commit.
> >
> > I queued the chipid as a dependency for ASV but ASV requires the
> > regmap. What would be left after reverting the regmap part? Simple
> > unused printk driver? No need for such. If reverting, then let's drop
> > entire driver and rework it offline.
>
> In fact there is now no dependency between the chipid and the ASV
> driver (patch 3/9), the regmap is provided by the syscon driver/API.
> I should have added "depends on REGMAP && MFD_SYSCON" to Kconfig.
> Both drivers (chipid, ASV) share the registers region so the regmap
> API seemed appropriate here.

Indeed, ASV needs only the header + DT change... Then actually we do
not need chipid driver at all. Just to print the SoC and provide sysfs
entry? If this is the only purpose, then it should be a driver.

> Converting the chipid code to platform driver wouldn't make sense as
> it wouldn't be useful early in arch/arm/mach-exynos and we can't have
> two drivers for same device (the ASV driver matches on the chipid
> compatible now).

There is no use case for arm/mach-exynos. This code was not
resubmitted and I doubt it will be (unless now someone wants to prove
I am wrong and sends it again :) ). The two-device case is indeed a
problem but it is possible. Clocks are doing it with PMU driver. See
CLK_OF_DECLARE_DRIVER(), although I do not remember whether it is
maybe obsolete pattern (discouraged).

Best regards,
Krzysztof