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

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Message-ID: <CAHp75VfVRa5m3WeEvMvGCRK7YRBD5BCxOL2DHDzyuQ1cD4J9UA@mail.gmail.com>
Date:   Wed, 7 Dec 2022 18:48:41 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     Tomer Maimon <tmaimon77@...il.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

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