linux-kernel - Re: [PATCH] mmc: Test bus-width for old MMC devices (v2)

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Date:	Tue, 21 Dec 2010 22:56:32 -0500
From:	zhangfei gao <zhangfei.gao@...il.com>
To:	Philip Rakity <prakity@...vell.com>
Cc:	Takashi Iwai <tiwai@...e.de>, Chris Ball <cjb@...top.org>,
	Aries Lee <arieslee@...cron.com>, Qiming Wu <wuqm@...vell.com>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: Test bus-width for old MMC devices (v2)

On Tue, Dec 21, 2010 at 11:36 AM, Philip Rakity <prakity@...vell.com> wrote:
>
>
> Can you please try this diff and see if it works for you.
>
> Will do formal patch after your testing.  What card is failing ?
>
> Please let me know the manufacturing information so can add card to my test suite.
>
> Philip
>
> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
> index 1d8409f..77072c8 100644
> --- a/drivers/mmc/core/mmc.c
> +++ b/drivers/mmc/core/mmc.c
> @@ -558,6 +558,8 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
>                                         EXT_CSD_BUS_WIDTH,
>                                         ext_csd_bits[idx][0]);
>                        if (!err) {
> +                               mmc_set_bus_width_ddr(card->host,
> +                                                     bus_width, MMC_SDR_MODE);
Test OK,
Curious why move here, then mmc_set_bus_width_ddr is called twice in
fact when ddr=0 &&  (!(host->caps & MMC_CAP_BUS_WIDTH_TEST)), though
not impact function.
mmc_set_bus_width is mmc_set_bus_width_ddr(host, width, MMC_SDR_MODE).

>                                /*
>                                 * If controller can't handle bus width test,
>                                 * use the highest bus width to maintain
> @@ -565,8 +567,6 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
>                                 */
>                                if (!(host->caps & MMC_CAP_BUS_WIDTH_TEST))
>                                        break;
> -                               mmc_set_bus_width_ddr(card->host,
> -                                                     bus_width, MMC_SDR_MODE);
>                                err = mmc_bus_test(card, bus_width);
>                                if (!err)
>                                        break;
> @@ -586,7 +586,8 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
>                } else if (ddr) {
>                        mmc_card_set_ddr_mode(card);
>                        mmc_set_bus_width_ddr(card->host, bus_width, ddr);
> -               }
> +               } else
> +                       mmc_set_bus_width (card->host, bus_width);
>        }
>
>        if (!oldcard)
>
>
> Philip
>
> On Dec 21, 2010, at 2:59 AM, zhangfei gao wrote:
>
>> On Fri, Dec 17, 2010 at 3:11 AM, Takashi Iwai <tiwai@...e.de> wrote:
>>> At Fri, 17 Dec 2010 03:43:42 +0000,
>>> Chris Ball wrote:
>>>>
>>>> Hi Philip,
>>>>
>>>> On Thu, Dec 16, 2010 at 06:33:49PM -0800, Philip Rakity wrote:
>>>>> It is not possible for bus_width to be not initialized.  This would imply ARRAY_SIZE(bus_widths) is 1.  Certainly not true.
>>>>
>>>> Right, I agree.  We should fix the warning anyway.
>>>
>>> Well, this is always a gray-zone question.  One prefers fixing it
>>> either via uninitialized_var() or by setting a bogus value.  But, this
>>> would cover any possible real bug in future.  Thus another prefers
>>> ignoring it, because it's just a compiler bug (mostly of old gcc).
>>>
>>> After all, it's up to maintainer, so take as you like :)
>>>
>>>
>>> thanks,
>>>
>>> Takashi
>>>
>>>
>>>>> We could just initialize by changing
>>>>> +           unsigned idx, bus_width;
>>>>> to
>>>>> +           unsigned idx, bus_width = 0;
>>>>
>>>> Okay, I've pushed to mmc-next with that change.
>>>>
>>>>> I wonder what compiler are you using so we can avoid this issue in future.
>>>>
>>>> Ah, good point -- I was building with a gcc 4.1.2 ARM cross-compiler,
>>>> and using a gcc 4.5.1 cross-build instead avoids the warning.
>>>>
>>>> Thanks,
>>>>
>>>> --
>>>> Chris Ball   <cjb@...top.org>   <http://printf.net/>
>>>> One Laptop Per Child
>>>>
>>>
>>
>> Could you help adding this modification?
>> We found error happen since bus_width is not set at these condition:
>> 1. ddr=0
>> 2. not set MMC_CAP_BUS_WIDTH_TEST
>>
>> diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c
>> index 1d8409f..86cac0d 100644
>> --- a/drivers/mmc/core/mmc.c
>> +++ b/drivers/mmc/core/mmc.c
>> @@ -586,7 +586,11 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr,
>>               } else if (ddr) {
>>                       mmc_card_set_ddr_mode(card);
>>                       mmc_set_bus_width_ddr(card->host, bus_width, ddr);
>> -             }
>> +
>> +             } else
>> +                     mmc_set_bus_width(card->host,
>> +                                     bus_widths[idx]);
>> +
>>       }
>>
>>       if (!oldcard)
>
>
--
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