On 01/02/2010 04:23 PM, Ben Nizette wrote:
On 02/01/2010, at 11:08 PM, Pierre Ossman wrote:
On Sat, 2 Jan 2010 20:07:01 +1100
Ben Nizette<b...@niasdigital.com> wrote:
Pierre, thoughts? All my cards were borderline spec but Hein's got a
mainstream, common card which seems to completely ignore the spec. Can we just
take the few-hundred-uS hit and allow initialization down at the bottom end,
say 100kHz?
Broken cards seem to be all over the spectrum, so I wouldn't be
suprised if you find ones that break if you go too low as well.
Yea good point, though given there might not even be a One Freq to Rule Them
All, how about:
---8<---
From: Ben Nizette<b...@niasdigital.com>
Subject: [PATCH v3] mmc: Make ID freq configurable
While the SD spec specifies a range of frequencies for the ID phase from
100-400kHz, not all cards play by the rules. This patch adds a Kconfig option
to allow the user to tweak this to their card/host config, though the default
of 250kHz should be fine for all spec-abiding cards and most others besides.
Signed-off-by: Ben Nizette<b...@niasdigital.com>
---
diff --git a/drivers/mmc/core/Kconfig b/drivers/mmc/core/Kconfig
index ab37a6d..a8e5003 100644
--- a/drivers/mmc/core/Kconfig
+++ b/drivers/mmc/core/Kconfig
@@ -14,3 +14,15 @@ config MMC_UNSAFE_RESUME
This option is usually just for embedded systems which use
a MMC/SD card for rootfs. Most people should say N here.
+config MMC_ID_FREQ
+ int "SD/MMC Card initialisation frequency (Hz)"
+ default 250000
+ help
+ The SD card specification allows for initialisation
+ frequencies from 100-400kHz however some broken cards are
+ known not to work across this whole range.
+
+ If you're having problems with a particular card not being
+ detected, you may try adjusting this frequency up or down
+ but for widest compatibility just leave it default.
Don't know that a kconfig option is best for this, it'd suck to have to
recompile the kernel to change it. Module option might be better..
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