mmc: warn about voltage mismatches

From: David Brownell <[email protected]>

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).

---
 drivers/mmc/core/core.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -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;
 	}
 

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.

Still, it's better than nothing.

Queued.

     -- Pierre Ossman

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

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