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

[Tomer Maimon]

Hi Andy and Adrian,

Thanks for your clarifications

On Mon, 5 Dec 2022 at 16:33, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> On 5/12/22 16:17, Andy Shevchenko wrote:
> > On Mon, Dec 5, 2022 at 4:14 PM Andy Shevchenko
> > <andy.shevchenko@xxxxxxxxx> wrote:
> >>
> >> On Mon, Dec 5, 2022 at 3:41 PM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
> >>> On 5/12/22 15:25, Andy Shevchenko wrote:
> >>>> On Mon, Dec 5, 2022 at 1:20 PM Tomer Maimon <tmaimon77@xxxxxxxxx> wrote:
> >>>>> On Mon, 5 Dec 2022 at 12:54, Andy Shevchenko <andy.shevchenko@xxxxxxxxx> wrote:
> >>>>>> On Mon, Dec 5, 2022 at 10:54 AM Tomer Maimon <tmaimon77@xxxxxxxxx> 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.
>
> 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_?
>
> >
> > 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.
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.
> >>>>
> >>>>> 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
> >
> >
> >
>

Best regards,

Tomer