linux-kernel - Re: [PATCH v2 2/2] mmc: sdhci-npcm: Add NPCM SDHCI driver

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Message-ID: <CAHp75VemBiGUTspEYDe3hwA9pEzjNMQGY6_kUoVMJyCuEWgChw@mail.gmail.com>
Date:   Mon, 5 Dec 2022 16:17:47 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     ulf.hansson@...aro.org, avifishman70@...il.com,
        tali.perry1@...il.com, joel@....id.au, venture@...gle.com,
        yuenn@...gle.com, benjaminfair@...gle.com,
        skhan@...uxfoundation.org, davidgow@...gle.com,
        pbrobinson@...il.com, gsomlo@...il.com, briannorris@...omium.org,
        arnd@...db.de, krakoczy@...micro.com, openbmc@...ts.ozlabs.org,
        linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tomer Maimon <tmaimon77@...il.com>
Subject: Re: [PATCH v2 2/2] mmc: sdhci-npcm: Add NPCM SDHCI driver

On Mon, Dec 5, 2022 at 4:14 PM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Mon, Dec 5, 2022 at 3:41 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
> > On 5/12/22 15:25, Andy Shevchenko wrote:
> > > On Mon, Dec 5, 2022 at 1:20 PM Tomer Maimon <tmaimon77@...il.com> wrote:
> > >> On Mon, 5 Dec 2022 at 12:54, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > >>> On Mon, Dec 5, 2022 at 10:54 AM Tomer Maimon <tmaimon77@...il.com> wrote:
>
> ...
>
> > >>>> +       pltfm_host->clk = devm_clk_get_optional(&pdev->dev, NULL);
> > >>>
> > >>> You can't mix devm with non-devm in this way.
> > >> Can you explain what you mean You can't mix devm with non-devm in this
> > >> way, where is the mix?
> > >> In version 1 used devm_clk_get, is it problematic?
> > >
> > > devm_ is problematic in your case.
> > > TL;DR: you need to use clk_get_optional() and clk_put().
> >
> > devm_ calls exactly those, so what is the issue?
>
> The issue is the error path or removal stage where it may or may be
> not problematic. To be on the safe side, the best approach is to make
> sure that allocated resources are being deallocated in the reversed
> order. That said, the
>
> 1. call non-devm_func()
> 2. call devm_func()
>
> is wrong strictly speaking.

To elaborate more, the

1. call all devm_func()
2. call only non-devm_func()

is the correct order.

Hence in this case the driver can be worked around easily (by
shuffling the order in ->probe() to call devm_ first), but as I said
looking into implementation of the _unregister() I'm pretty sure that
clock management should be in sdhci-pltfm, rather than in all callers
who won't need the full customization.

Hope this helps to understand my point.

> > > Your ->remove() callback doesn't free resources in the reversed order
> > > which may or, by luck, may not be the case of all possible crashes,
> > > UAFs, races, etc during removal stage. All the same for error path in
> > > ->probe().
>
> I also pointed out above what would be the outcome of neglecting this rule.
>
> > >>>> +       if (IS_ERR(pltfm_host->clk))
> > >>>> +               return PTR_ERR(pltfm_host->clk);
> > >>>> +
> > >>>> +       ret = clk_prepare_enable(pltfm_host->clk);
> > >>>> +       if (ret)
> > >>>> +               return ret;
> > >>>> +
> > >>>> +       caps = sdhci_readl(host, SDHCI_CAPABILITIES);
> > >>>> +       if (caps & SDHCI_CAN_DO_8BIT)
> > >>>> +               host->mmc->caps |= MMC_CAP_8_BIT_DATA;
> > >>>> +
> > >>>> +       ret = mmc_of_parse(host->mmc);
> > >>>> +       if (ret)
> > >>>> +               goto err_sdhci_add;
> > >>>> +
> > >>>> +       ret = sdhci_add_host(host);
> > >>>> +       if (ret)
> > >>>> +               goto err_sdhci_add;
> > >>>
> > >>> Why can't you use sdhci_pltfm_register()?
> > >> two things are missing in sdhci_pltfm_register
> > >> 1. clock.
> > >
> > > Taking into account the implementation of the corresponding
> > > _unregister() I would add the clock handling to the _register() one.
> > > Perhaps via a new member of the platform data that supplies the name
> > > and index of the clock and hence all clk_get_optional() / clk_put will
> > > be moved there.
> > >
> > >> 2. Adding SDHCI_CAN_DO_8BIT capability according the eMMC capabilities.
> > >
> > > All the same, why can't platform data be utilised for this?
> > >
> > >>>> +       return 0;
> > >>>> +
> > >>>> +err_sdhci_add:
> > >>>> +       clk_disable_unprepare(pltfm_host->clk);
> > >>>> +       sdhci_pltfm_free(pdev);
> > >>>> +       return ret;
> > >>>> +}
>
>
> --
> With Best Regards,
> Andy Shevchenko



-- 
With Best Regards,
Andy Shevchenko