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SubjectRE: [PATCH] mmc: align data size for host which only supports power-of-2 block
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>


>-----Original Message-----
>From: Pierre Ossman [mailto:drzeus-mmc@drzeus.cx]
>Sent: Sunday, March 15, 2009 4:31 AM
>To: Bryan Wu
>Cc: linux-kernel@vger.kernel.org; Cai, Cliff; Bryan Wu
>Subject: Re: [PATCH] mmc: align data size for host which only
>supports power-of-2 block
>
>On Fri, 6 Mar 2009 11:15:21 +0800
>Bryan Wu <cooloney@kernel.org> wrote:
>
>> From: Cliff Cai <cliff.cai@analog.com>
>>
>> Signed-off-by: Cliff Cai <cliff.cai@analog.com>
>> Signed-off-by: Bryan Wu <cooloney@kernel.org>
>> ---
>
>This patch seems premature as there is no associated
>modification of any of the host drivers.

The SDH on Blackfin BF54x/BF51x only supports power-of-2 block
transfer,we will soon
Send the sdh driver to mainline as well.

>
>> drivers/mmc/core/core.c | 8 +++++++-
>> include/linux/mmc/host.h | 1 +
>> 2 files changed, 8 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c index
>> df6ce4a..15119df 100644
>> --- a/drivers/mmc/core/core.c
>> +++ b/drivers/mmc/core/core.c
>> @@ -321,7 +321,13 @@ unsigned int mmc_align_data_size(struct
>mmc_card *card, unsigned int sz)
>> * the core about its problems yet, so for now we just 32-bit
>> * align the size.
>> */
>> - sz = ((sz + 3) / 4) * 4;
>> +
>> + /* Align size for host which only supports power-of-2 block */
>> + if (card->host->powerof2_block) {
>> + if (sz & (sz - 1))
>> + sz = 1 << fls(sz);
>> + } else
>> + sz = ((sz + 3) / 4) * 4;
>>
>> return sz;
>> }
>
>At the very least, the comment at the top of this function
>must go. But really, if we want to improve this we should
>probably do it properly and have flags for the different
>limitations that are available.
>Padding to a power of two size can also mean a rather large
>padding. We might need to check the host data limits after
>doing the adjustment.

Yes,but it's the higher level driver's job.

>
>> diff --git a/include/linux/mmc/host.h
>b/include/linux/mmc/host.h index
>> 4e45725..7416ed1 100644
>> --- a/include/linux/mmc/host.h
>> +++ b/include/linux/mmc/host.h
>> @@ -162,6 +162,7 @@ struct mmc_host {
>> struct dentry *debugfs_root;
>>
>> unsigned long private[0] ____cacheline_aligned;
>> + unsigned int powerof2_block; /* host only
>supports power-of-2 block */
>> };
>>
>> extern struct mmc_host *mmc_alloc_host(int extra, struct device *);
>
>This is just broken. Putting it after private completely
>breaks accesses to the host driver private data.

Sure,it should be added before private.

Thanks

Cliff


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