Raspberry Pi Compute Module

[Martin Sperl]

> On 27.08.2015, at 20:04, Martin Sperl <martin at sperl.org> wrote:
> 
> 
> 
>> On 27.08.2015, at 18:11, Stephen Warren <swarren at wwwdotorg.org> 
>>> Compiling the kernel with mmc as module plus mmc-debug enabled gives the
>>> below:
>>> after loading the driver:
>> ...
>>> [   69.432782] mmc0: clock 400000Hz busmode 2 powermode 2 cs 0 Vdd 21
>>> width 0 timing 0
>> 
>> ... lot of working commands ...
>> 
>>> [   69.499732] mmc0: clock 25000000Hz busmode 2 powermode 2 cs 0 Vdd 21
>>> width 0 timing 0
>> 
>> (up until now, the clock has always be 400KHz, not it's 25MHz)
>> 
>>> [   69.499854] mmc0: starting CMD6 arg 03a10101 flags 0000049d
>>> [   69.499924] sdhci [sdhci_irq()]: *** mmc0 got interrupt: 0x00038000
>>> [   69.499982] mmc0: req failed (CMD6): -110, retrying...
>>> [   69.500041] sdhci [sdhci_irq()]: *** mmc0 got interrupt: 0x00038000
>>> [   69.500091] mmc0: req failed (CMD6): -110, retrying...
>>> [   69.500146] sdhci [sdhci_irq()]: *** mmc0 got interrupt: 0x00038000
>>> [   69.500188] mmc0: req failed (CMD6): -110, retrying...
>>> [   69.500251] sdhci [sdhci_irq()]: *** mmc0 got interrupt: 0x00038000
>>> [   69.500300] mmc0: req done (CMD6): -110: 00000000 00000000 00000000
>>> 00000000
>>> [   69.500345] mmc0: error -110 whilst initialising MMC card
>> 
>> My guess it that the clock rate change caused this, not the CMD6 itself?
> 
> I saw a patch for one device that required more delay (in the order of 100us) between cmd13 and cmd6 - can't pinpoint it right now...
> 
> But then logging would add some delays, but maybe not enough...
> 
> Maybe changing clock to 400khz would allow access to the device - even if it is slow...
> 
> Can we configure that with the device tree, just to see if it makes a difference?
> 
See here: https://lkml.org/lkml/2014/9/9/382
for one device that required it...

Martin