Re: When bus width detection procedure takes place, kernel cannot lock on correct bus width

From: Chris Ball <cjb@laptop.org>
To: elad.yi@gmail.com
Cc: linux-mmc@vger.kernel.org, Philip Rakity <prakity@nvidia.com>
Subject: Re: When bus width detection procedure takes place, kernel cannot lock on correct bus width
Date: Fri, 22 Mar 2013 13:06:45 -0400	[thread overview]
Message-ID: <87wqszl5y2.fsf@octavius.laptop.org> (raw)
In-Reply-To: <87ip4qdybr.fsf@octavius.laptop.org> (Chris Ball's message of "Sun, 17 Mar 2013 08:07:20 -0400")

Hi,

On Sun, Mar 17 2013, Chris Ball wrote:
> I've been working on a bringup of an new board in Harmonic Inc.
> This board uses Sandisk iNand eMMC flash.
> I've noticed that the mmc driver keeps detecting 1 bit width although HW
> supports 4 bit, looked into it, and found the problem. In line 571 at mmc.c:
> There is:
>     /* only compare read only fields */
>     err = !((card->ext_csd.raw_partition_support ==
>             bw_ext_csd[EXT_CSD_PARTITION_SUPPORT]) &&
>         (card->ext_csd.raw_erased_mem_count ==
>             bw_ext_csd[EXT_CSD_ERASED_MEM_CONT]) &&
>         (card->ext_csd.rev ==
>             bw_ext_csd[EXT_CSD_REV]) &&
>         (card->ext_csd.raw_ext_csd_structure ==
>                 ...
>
> The problem is that raw_partition_support is not the same when setting width of
> 4 bits instead of 1 bit, and shouldn't be compared at all although it is read
> only.
> this should be changed to:
>     /* only compare read only fields */
>     err = !((card->ext_csd.raw_erased_mem_count ==
>             bw_ext_csd[EXT_CSD_ERASED_MEM_CONT]) &&
>         (card->ext_csd.rev ==
>             bw_ext_csd[EXT_CSD_REV]) &&
>         (card->ext_csd.raw_ext_csd_structure ==
>                 ...

Philip, what do you think?

Thanks,

- Chris.
-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>
One Laptop Per Child