[U-Boot] [RFC] mmc: Properly determine maximum supported bus width

[Fleming Andy-AFLEMING]

Yes, I'm processing my queue today.

On Nov 26, 2012, at 17:27, "Stephen Warren" <swarren at wwwdotorg.org> wrote:

> On 10/31/2012 11:02 PM, Andy Fleming wrote:
>> At some point, a confusion arose about the use of the bit
>> definitions in host_caps for bus widths, and the value
>> in ext_csd. By coincidence, a simple shift could convert
>> between one and the other:
>> 
>> MMC_MODE_1BIT = 0, EXT_CSD_BUS_WIDTH_1 = 0
>> MMC_MODE_4BIT = 0x100, EXT_CSD_BUS_WIDTH_4 = 1
>> MMC_MODE_8BIT = 0x200, EXT_CSD_BUS_WIDTH_8 = 2
>> 
>> However, as host_caps is a bitmask of supported things,
>> there is not, in fact, a one-to-one correspondence. host_caps
>> is capable of containing MODE_4BIT | MODE_8BIT, so nonsensical
>> things were happening where we would try to set the bus width
>> to 12.
>> 
>> The new code clarifies the very different namespaces:
>> 
>> host_caps/card_caps = bitmask (MMC_MODE_*)
>> ext CSD fields are just an index (EXT_CSD_BUS_WIDTH_*)
>> mmc->bus_width integer number of bits (1, 4, 8)
>> 
>> We create arrays to map between the namespaces, like in Linux.
> 
> Andy, is this patch likely to get merged soon to u-boot.git branch
> master? Unfortunately, some Tegra patches that ideally rely on this
> patch being present have already been applied and merged into
> u-boot-arm.git branch master.
>