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Re: RFC: PCI SD host controller driver & mmc/mmcsd modules improvements

M. Warner Losh wrote:
: Problem was solved by increasing the number of answer read attempts in mmc_send_app_op_cond(). With attached patch (against latest driver version) card is recognized properly on ~ 190th attempt (while in original driver there are only 100 attempts).
: : Furthermore, non-mine SDHC card is now also recognized in this cardreader (it doesn't even under Windows). In this case, it takes about 400 attempts to read answer.

I think I bumped the number of iterations to 100 when I found that 10
wasn't enough.  25 different cards worked just fine, but I got use of
a 16MB SD card at BSDcan that needed like 65.  Bumping it from 100 to
1000, however, makes the timeout go from 1s to 10s.  That opens up
window for insertion races, but that's the only downside I see...  Of
course, we want to fix those races, but this may expose them a little

I can't believe that you had a card that took 4s to become active!

Can you confirm the elapsed time is really 4s for that card?
Otherwise, this may be pointing out a bug in another area of the

Completely fortunate I have noticed that number of iterations depends on my laptop power source. After small investigation I have found that it actually depends on dev.cpu.0.freq value. With default value 2400 I have only several iterations. But every double frequency decrease doubles iteration count. With minimum value 100MHz I have more then 100 iterations. Same time it doesn't looks like this time is a real wall time. It looks like DELAY() used in a loop has some problems with time counting.

Alexander Motin
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