Re: [PATCH] mmc: fix incorrect interpretation of card type bits

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 19 Mar 2010 08:24:56 +0200
Adrian Hunter <adrian.hunter@nokia.com> wrote:

> From: Adrian Hunter <adrian.hunter@nokia.com>
> Date: Fri, 19 Mar 2010 08:06:54 +0200
> Subject: [PATCH] mmc: fix incorrect interpretation of card type bits
> 
> In the extended CSD register the CARD_TYPE is an 8-bit value
> of which the upper 6 bits were reserved in JEDEC specifications
> prior to version 4.4.  In version 4.4 two of the reserved bits
> were designated for identifying support for the newly added
> High-Speed Dual Data Rate.  Unfortunately the mmc_read_ext_csd()
> function required that the reserved bits be zero instead of
> ignoring them as it should.
> 
> This patch makes mmc_read_ext_csd() ignore the CARD_TYPE bits
> that are reserved or not yet supported.  It also stops the
> function jumping to the end as though an error occurred, when
> it is only warns that the CARD_TYPE bits (that it does interpret)
> are invalid.

I need to whine about the changelog again.

I'm guessing that the effect here is that if someone puts one of these
new cards into an old kernel, this card will be incorrectly handled. 
Perhaps in ways which render the whole thing useless.

If that was a good guess then this patch would be needed in earlier
kernels too.

But it was only a guess, and I'd prefer not to have to guess.  So
please do remember to explain things like this in the changelog?