linux-kernel - Re: [PATCH v4 2/3] mmc: core: Factor out the alignment of erase size

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Date:   Tue, 6 Sep 2016 10:52:01 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Baolin Wang <baolin.wang@...aro.org>, Andreas Mohr <andi@...as.de>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Russell King <rmk+kernel@....linux.org.uk>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Douglas Anderson <dianders@...omium.org>,
        Heiko Stübner <heiko@...ech.de>,
        David Jander <david@...tonic.nl>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v4 2/3] mmc: core: Factor out the alignment of erase size

On 6/09/2016 9:26 a.m., Baolin Wang wrote:
> Hi Andreas,
>
> On 6 September 2016 at 12:34, Andreas Mohr <andi@...as.de> wrote:
>> On Tue, Sep 06, 2016 at 10:55:11AM +0800, Baolin Wang wrote:
>>> In order to clean up the mmc_erase() function and do some optimization
>>> for erase size alignment, factor out the guts of erase size alignment
>>> into mmc_align_erase_size() function.
>>>
>>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>>> Tested-by: Shawn Lin <shawn.lin@...k-chips.com>
>>> ---
>>>   drivers/mmc/core/core.c |   60 +++++++++++++++++++++++++++++------------------
>>>   1 file changed, 37 insertions(+), 23 deletions(-)
>>>
>>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
>>> index 7d7209d..5f93eef 100644
>>> --- a/drivers/mmc/core/core.c
>>> +++ b/drivers/mmc/core/core.c
>>> @@ -2202,6 +2202,37 @@ out:
>>>        return err;
>>>   }
>>>
>>> +static unsigned int mmc_align_erase_size(struct mmc_card *card,
>>> +                                      unsigned int *from,
>>> +                                      unsigned int *to,
>>> +                                      unsigned int nr)
>>> +{
>>> +     unsigned int from_new = *from, nr_new = nr, rem;
>>> +
>>> +     rem = from_new % card->erase_size;
>>> +     if (rem) {
>>> +             rem = card->erase_size - rem;
>>> +             from_new += rem;
>>> +             if (nr_new > rem)
>>> +                     nr_new -= rem;
>>> +             else
>>> +                     return 0;
>>> +     }
>>> +
>>> +     rem = nr_new % card->erase_size;
>>> +     if (rem)
>>> +             nr_new -= rem;
>>> +
>>> +     if (nr_new == 0)
>>> +             return 0;
>>> +
>>> +     /* 'from' and 'to' are inclusive */
>>> +     *to = from_new + nr_new - 1;
>>> +     *from = from_new;
>>> +
>>> +     return nr_new;
>>> +}
>>> +
>>>   /**
>>>    * mmc_erase - erase sectors.
>>>    * @card: card to erase
>>> @@ -2234,31 +2265,14 @@ int mmc_erase(struct mmc_card *card, unsigned int from, unsigned int nr,
>>>        }
>>>
>>>        if (arg == MMC_ERASE_ARG) {
>>> -             rem = from % card->erase_size;
>>> -             if (rem) {
>>> -                     rem = card->erase_size - rem;
>>> -                     from += rem;
>>> -                     if (nr > rem)
>>> -                             nr -= rem;
>>> -                     else
>>> -                             return 0;
>>> -             }
>>> -             rem = nr % card->erase_size;
>>> -             if (rem)
>>> -                     nr -= rem;
>>> +             nr = mmc_align_erase_size(card, &from, &to, nr);
>>> +             if (nr == 0)
>>> +                     return 0;
>>> +     } else {
>>> +             /* 'from' and 'to' are inclusive */
>>> +             to -= 1;
>>>        }
>>>
>>> -     if (nr == 0)
>>> -             return 0;
>>> -
>>> -     to = from + nr;
>>> -
>>> -     if (to <= from)
>>> -             return -EINVAL;
>>
>> Hmm, this is swallowing -EINVAL behaviour
>> i.e., now possibly violating protocol?
>
> I didn't see what situation will make variable 'to' is less than
> 'from' since I think variable 'nr' is always larger than 0, right? If
> so, we should remove this useless checking. Thanks.

It is checking overflows.

>
>>
>> (this may easily be ok - haven't done an extensive review -
>> but since the commit has that characteristic change,
>> the commit message should contain that detail)
>>
>> Thanks for the cleanup work & HTH,
>>
>> Andreas Mohr
>
>
>