Comment 10 for bug 1307674

Ah, I was cheering prematurely, sorry.

It seems that the mentioned patch did not effect the observed change in behavior, so presumably something has changed in the stock Ubuntu kernel to do this.

The currently observed behavior with stock ubuntu (3.13.0-24-generic) as well as my patched kernel (3.13.0-27-generic with patch) is the following:

 1. After a reboot, I can plug in the card and stuff is working (automatic mouting, etc)
 2. The transfer rate (for reading) seems to be capped at 20 MB/s (I tested with the same rsync command in OS X, and got nearly 50 MB/s. The card is advertised as 30 MB/s)
 3. After removing the card, subsequent inserts of the card do not work. I can only use the card one time after a reboot.
 4. Similarly as 3., with system sleep. If I let the system sleep and then wake it up, the card reader does not work.

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Observations from dmesg:

When the reader works, I get the following messages in dmesg, which are absent when the reader does not work: "mmc0: Skipping voltage switch". This is followed by "mmc0: new high speed SDHC card at address 59b4". Notice that the card is incorrectly recognized as "high speed SDHC".

When the reader fails, I get the following mesages in dmesg, which are absent when the reader does work: "sdhci: Timeout waiting for Buffer Read Ready interrupt during tuning procedure, falling back to fixed sampling clock". This is followed by "mmc0: new ultra high speed SDR104 SDHC card at address 59b4". Notice that this time, the card is correctly identified as "ultra high speed SDHC".

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It looks like it might be the case that the driver fails if and only if the card is "ultra high speed", unless the driver mistakenly believes that the card is merely "high speed".

Is it possible to ask the driver to not attempt UHS mode?