[MX25][MMC] mmc esdhc failure in 3.3

[joancarles]

Hi

>> Might be unrelated, however I have been keeping my eyes on the fix 
>> of
>> ENGcm07207 quirk introduced with 16a790bcc. According to the
>> IMX25CE.pdf, to abort data transfers on the AHB, software can reset 
>> the
>> eSDHC by writing 1 to SYSCTL[24] (RSTA), which currently is not done
>> with SDHCI_QUIRK_NO_MULTIBLOCK. It sets the max_blk_count to 1 
>> instead
>> of 65535. Not sure if this is also limiting the speed.
>>
> I tried to increase max_blk_count and it breaks after a few tests.

I will redo your tests in a jiffy, however the latency issues worry me 
a wee bit.

> Using an oscilloscope it seems we have a big latency between each
> transfer which could explain the low throughput, I didn't have the
> time to look deeper at this problem.

The latency we can see here in the oscilloscope is tremendous between 
two CMD24: 8ms! What is causing this? It is certainly unrelated to the 
MULTIBLOCK feature. Having a clock at 33.25MHz, our maximal read, as 
confirmed by dd is:

33.25[MHz] * 4[bits data] / 8[bits/Byte] * 30 [us write] / 8000 [us 
sleep] =~ 60KB/s

So, what's keeping the driver 8ms from sending the data??? Any pointers 
on where I could twiddle some bits in the driver? Where do I start 
looking?

Cheers
-- 
Joan C. Abelaira