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

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Message-ID: <CAP6Zq1hj1YikzsY8bKMayYErQomMEGC6V3_6DUOo67=L4yfQrQ@mail.gmail.com>
Date:   Thu, 8 Dec 2022 14:58:44 +0200
From:   Tomer Maimon <tmaimon77@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>, 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
Subject: Re: [PATCH v2 2/2] mmc: sdhci-npcm: Add NPCM SDHCI driver

Thanks a lot, Adrian and andy!

Appreciate it

On Wed, 7 Dec 2022 at 18:49, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
>
> On Wed, Dec 7, 2022 at 3:49 PM Adrian Hunter <adrian.hunter@...el.com> wrote:
> > On 7/12/22 15:25, Andy Shevchenko wrote:
> > > On Wed, Dec 7, 2022 at 3:01 PM Tomer Maimon <tmaimon77@...il.com> wrote:
> > >> On Mon, 5 Dec 2022 at 16:33, Adrian Hunter <adrian.hunter@...el.com> wrote:
> > >>> On 5/12/22 16:17, Andy Shevchenko wrote:
> > >>>> 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:
>
> ...
>
> > >>>>>>> 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.
> > >>>
> > >>> 1. WRT pltfm_host->clk, that is what is happening
> > >>> 2. WRT other resources that is simply not always possible because not every resource is wrapped by devm_
> > >>> e.g. mmc_alloc_host() / mmc_free_host()
> > >> I little confused about what to decide, should I use only
> > >> non-devm_func because mmc_alloc_host() / mmc_free_host() is not
> > >> warrped with devm_?
> > >
> > > It is up to you how to proceed. I pointed out the problem with your
> > > code which may or may not be fatal.
> > >
> > > If you want to solve it, there are several approaches:
> > > 1) get rid of devm_ completely;
> > > 2) properly shuffle the ordering in ->probe(), so all devm_ calls are
> > > followed by non-devm_;
> > > 3) wrap non-devm_ cals to become managed (see
> > > devm_add_action_or_reset() approach);
> > > 4) fix SDHCI / MMC layer by providing necessary devm_ calls and/or fix
> > > sdhci_pltfm_register() to handle the clock.
> >
> > I can take care of sdhci_pltfm when I next have some time.
> > Otherwise it looks OK to me, so I am acking it.
>
> Thank you!
>
> > > Personally, the list order is from the least, what I prefer, to the
> > > most (i.o.w. I would like to see rather 4) than 1) to be implemented).
> > >
> > >>>> 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.
>
> ...
>
> > >>>>>>>>> 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.
> > >> Do you mean to add it to sdhci_pltfm_register function? if yes I
> > >> believe it will take some time to modify sdhci_pltfm_register
> > >> I prefer not to use sdhci_pltfm_register.
> > >
> > > In the Linux kernel we are trying hard to avoid code duplication. Why
> > > do you need it to be open coded? (Yes, I heard you, but somebody
> > > should fix the issues with that funcion at some point, right?)
> > >
> > >>>>>>>> 2. Adding SDHCI_CAN_DO_8BIT capability according the eMMC capabilities.
> > >>>>>>>
> > >>>>>>> All the same, why can't platform data be utilised for this?
>
> --
> With Best Regards,
> Andy Shevchenko