linux-kernel - Re: [PATCH] mmc: Added quirks for Ricoh 1180:e823 lower base clock frequency

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Date:	Wed, 21 Nov 2012 19:29:46 -0500
From:	Chris Ball <cjb@...top.org>
To:	Manoj Iyer <manoj.iyer@...onical.com>
Cc:	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	jbarnes@...tuousgeek.org, matsumur@....ricoh.co.jp,
	linux-pci@...r.kernel.org, linux-mmc@...r.kernel.org
Subject: Re: [PATCH] mmc: Added quirks for Ricoh 1180:e823 lower base clock frequency

Hi Manoj, Matsumuro-san,

On Mon, Jul 18 2011, Manoj Iyer wrote:
> Right, without the patch I get..
>
> [   52.526665] mmc0: new SDHC card at address e624
> [   52.571228] mmcblk0: mmc0:e624 SD16G 14.8 GiB
> [   52.591071] mmcblk0: retrying using single block read
> [   52.593105] mmcblk0: error -84 transferring data, sector 0, nr 8,
> card status 0x900
> [   52.593109] end_request: I/O error, dev mmcblk0, sector 0
> [   52.594594] mmcblk0: error -84 transferring data, sector 1, nr 7,
> card status 0x900
> [   52.594604] end_request: I/O error, dev mmcblk0, sector 1
> [   52.602893] quiet_error: 24 callbacks suppressed
> [   52.602902] Buffer I/O error on device mmcblk0, logical block 0
> [   52.605349] ldm_validate_partition_table(): Disk read failed.
> [   52.605384] Dev mmcblk0: unable to read RDB block 0
> [   52.607729]  mmcblk0: unable to read partition table
> u@u:~$
>
> So, I cannot generate any comparison data with this SD card.

I don't know if you remember this bug, but I have reports from two users
who see "error -84"s on :e823 controllers even with this patch active on
modern ThinkPads.

Maybe 50MHz isn't low enough sometimes?  Is it possible to lower the base
clock further?

I noticed that the frequency is encoded ine one of the PCI writes:
+        * 0x32  - 50Mhz new clock frequency

So if I get access to one of these systems, I might try lowering that
value (by half, say) and see what happens.  But at the moment I haven't
found someone who's willing to try kernel patches yet, and I don't have
one of these systems myself.

Thanks!

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