[U-Boot] [PATCH/RFC] drivers/mmc/mmc.c: change the controller frequency before the card frequency

[U-Boot] [PATCH/RFC] drivers/mmc/mmc.c: change the controller frequency before the card frequency

[Albin Tonnerre]

While rewriting the atmel_mci driver to use the new MMC_GENERIC API (and allow
the use of SD/MMC on AT91 in the process), it appeared that switching the card
frequency before the controller frequency resulted in the answer from the card
never being received. Changing the controller frequency before the controller
frequency fixes that.

Signed-off-by: Albin Tonnerre <albin.tonnerre@free-electrons.com>
---
I'm sending this as an RFC, as I only own AT91-based boards. Therefore, I don't
know whether doing so breaks the code for other cards or not. Andy, do you see
any obvious problem with such a change ? Haavard: I did not find evidence of
such a requirement in the AT91SAM9G20 datasheet, is it known behaviour, or do
you think I'm doing something wrong that might cause this ?

 drivers/mmc/mmc.c |   16 ++++++++--------
 1 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/mmc/mmc.c b/drivers/mmc/mmc.c
index b69ce15..6ff3624 100644
--- a/drivers/mmc/mmc.c
+++ b/drivers/mmc/mmc.c
@@ -717,14 +717,6 @@ int mmc_startup(struct mmc *mmc)
 	if (err)
 		return err;
 
-	if (IS_SD(mmc))
-		err = sd_change_freq(mmc);
-	else
-		err = mmc_change_freq(mmc);
-
-	if (err)
-		return err;
-
 	/* Restrict card's capabilities by what the host can do */
 	mmc->card_caps &= mmc->host_caps;
 
@@ -786,6 +778,14 @@ int mmc_startup(struct mmc *mmc)
 			mmc_set_clock(mmc, 20000000);
 	}
 
+	if (IS_SD(mmc))
+		err = sd_change_freq(mmc);
+	else
+		err = mmc_change_freq(mmc);
+
+	if (err)
+		return err;
+
 	/* fill in device description */
 	mmc->block_dev.lun = 0;
 	mmc->block_dev.type = 0;
-- 
1.6.0.4

[U-Boot] [PATCH/RFC] drivers/mmc/mmc.c: change the controller frequency before the card frequency

[Jean-Christophe PLAGNIOL-VILLARD]

On 14:16 Wed 19 Aug     , Albin Tonnerre wrote:
> While rewriting the atmel_mci driver to use the new MMC_GENERIC API (and allow
> the use of SD/MMC on AT91 in the process), it appeared that switching the card
> frequency before the controller frequency resulted in the answer from the card
> never being received. Changing the controller frequency before the controller
> frequency fixes that.
IIRC it's not correct you are supposed to switch the card to higherfreq and
then the bus speed

could show the patch of the atmel_mci to help

Best Regards,
J.

[U-Boot] [PATCH/RFC] drivers/mmc/mmc.c: change the controller frequency before the card frequency

[Albin Tonnerre]

On Thu, Aug 20, 2009 at 01:42:04AM +0200, Jean-Christophe PLAGNIOL-VILLARD wrote :
> On 14:16 Wed 19 Aug     , Albin Tonnerre wrote:
> > While rewriting the atmel_mci driver to use the new MMC_GENERIC API (and allow
> > the use of SD/MMC on AT91 in the process), it appeared that switching the card
> > frequency before the controller frequency resulted in the answer from the card
> > never being received. Changing the controller frequency before the controller
> > frequency fixes that.
> IIRC it's not correct you are supposed to switch the card to higherfreq and
> then the bus speed

This was an error on my side, sorry for the noise.

> could show the patch of the atmel_mci to help

It's not complete yet, but I'll be sure to post it for comments as soon as i'm
done.

> Best Regards,
> J.

Regards,
-- 
Albin Tonnerre, Free Electrons
Kernel, drivers and embedded Linux development,
consulting, training and support.
http://free-electrons.com
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