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

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Date:   Mon, 5 Dec 2022 16:33:18 +0200
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Andy Shevchenko <andy.shevchenko@...il.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 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:
>>>>> 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.

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()

> 
> 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
> 
> 
>