[patch 2.6.28] mmc: warn about voltage mismatches

[patch 2.6.28] mmc: warn about voltage mismatches

[David Brownell]

From: David Brownell <dbrownell@users.sourceforge.net>

Get rid of a silent failure mode when the MMC/SD host doesn't
support the voltages needed to operate a given card, by
adding a warning.  A 3.3V host and a 3.0V card, for example,
no longer need to mysteriously just not work at all.

This isn't the best diagnostic; ideally it would also tell
what voltage the card and host support (and not just by
dumping the bitmasks).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
---
 drivers/mmc/core/core.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/mmc/core/core.c
+++ b/drivers/mmc/core/core.c
@@ -467,6 +467,8 @@ u32 mmc_select_voltage(struct mmc_host *
 		host->ios.vdd = bit;
 		mmc_set_ios(host);
 	} else {
+		pr_warning("%s: host doesn't support card's voltages\n",
+				mmc_hostname(host));
 		ocr = 0;
 	}
 

Re: [patch 2.6.28] mmc: warn about voltage mismatches

[Pierre Ossman]

On Wed, 31 Dec 2008 09:50:30 -0800
David Brownell <david-b@pacbell.net> wrote:

> From: David Brownell <dbrownell@users.sourceforge.net>
> 
> Get rid of a silent failure mode when the MMC/SD host doesn't
> support the voltages needed to operate a given card, by
> adding a warning.  A 3.3V host and a 3.0V card, for example,
> no longer need to mysteriously just not work at all.
> 

Hmm... I have sort of always assumed that 3.3V was always required by
the host and card, but re-reading the specs that clearly isn't the case.

> This isn't the best diagnostic; ideally it would also tell
> what voltage the card and host support (and not just by
> dumping the bitmasks).
> 

Still, it's better than nothing.

> Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
> ---

Queued.

-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  rdesktop, core developer          http://www.rdesktop.org

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