linux-kernel - Re: [RFC 0/4] clk/driver: platform: Fix kfree() of const memory on setting driver

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Date:   Mon, 18 Feb 2019 12:14:29 +0100
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Russell King <linux@...linux.org.uk>,
        Mark Brown <broonie@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        Tomasz Figa <tomasz.figa@...il.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Kukjin Kim <kgene@...nel.org>,
        Andy Gross <andy.gross@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm@...r.kernel.org,
        ALSA Development Mailing List <alsa-devel@...a-project.org>
Subject: Re: [RFC 0/4] clk/driver: platform: Fix kfree() of const memory on
 setting driver_override

On Mon, 18 Feb 2019 at 11:40, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> Hi Krzysztof,
>
> On Mon, Feb 18, 2019 at 11:27 AM Krzysztof Kozlowski <krzk@...nel.org> wrote:
> > The problem
> > ===========
> > Several device types (platform, amba, spi etc.) provide a driver_override
> > field.  On sysfs store or during device removal, they kfree() the
> > existing value.
> >
> > However the users are unaware of this and set the driver_override like:
> >
> >         pdev->driver_override = "exynos5-subcmu";
> >
> > which obviously leads to error.
>
> IMHO driver_override is not meant to be set by a driver, only from userspace,
> for binding the device to vfio (is there another use case?).
>
> >   clk: samsung: exynos5: Fix kfree() of const memory on setting
> >     driver_override
> >   slimbus: ngd: Fix kfree() of const memory on setting driver_override
>
> I see all users set override immediately after allocating a platform device.
> Can't they just allocate a platform device using the override name instead?
> What am I missing?

For the clk-exynos5-subcmu.c case, driver registers several
sub-devices. Each sub-devices is a clock controller associated with
power domain. I guess the author wanted to have meaningful names of
these sub-devices (DISP, CAM etc. like names of power domains),
instead of just exynos5-subcmu.1, exynos5-subcmu.2 ...

If driver_override should not be used for such case, then I could
replace it with what you said.

For the other uses of driver_override (drivers/rpmsg/rpmsg_internal.h
and drivers/slimbus/qcom-ngd-ctrl.c) I don't know.

Best regards,
Krzysztof