On 12/10/2012 1:51 PM, Johan Rudholm wrote:
Hi Subhash,
2012/12/8 Subhash Jadavani <subhashj@xxxxxxxxxxxxxx>:
On 12/7/2012 9:49 PM, Johan Rudholm wrote:
When switching SD and SDIO cards from 3.3V to 1.8V signal levels, the
clock should be gated for 5 ms during the step. After enabling the
clock, the host should wait for at least 1 ms before checking for
failure. Failure by the card to switch is indicated by dat[0:3] being
pulled low. The host should check for this condition and power-cycle
the card if failure is indicated.
Add a retry mechanism for the SDIO case.
If the voltage switch fails repeatedly, give up and continue the
initialization using the original voltage.
This patch places a couple of requirements on the host driver:
1) mmc_set_ios with ios.clock = 0 must gate the clock
2) mmc_power_off must actually cut the power to the card
if these requirements are not fulfilled, the 1.8V signal voltage switch
may not be successful.
<snip>
err = host->ops->start_signal_voltage_switch(host,
&host->ios);
Shouldn't you fix all the existing host drivers who have already implemented
start_signal_voltage_switch host ops? If you don't change them as part of
this patch then
i afraid UHS functionality would be broken on those platforms. Also, it's
not just changing the start_signal_voltage_switch hot op implementation, you
may also need to add card_busy() host op implementation for those drivers.
This is true, and I did actually make an RFC for the sdhci driver
("[RFC] mmc: sdhci: Let core handle UHS switch failure":
https://patchwork.kernel.org/patch/1517211/). Daniel Drake tried this
code for a problem related to the 1.8V switch (his board could
actually not perform the switch to 1.8V even though this capability
was announced), and I think this pointed out two areas for further
investigation before a proper patch for the sdhci driver can be
created:
1) the sdhci driver may not gate the clock when setting ios.clock = 0
and calling mmc_set_ios
2) mmc_power_off may not cut power to the card
maybe 2) was only for Daniel's board, I'm not sure, but this needs to
be investigated further anyway. Since I don't have any sdhci hardware
with UHS support, this must either be done by some other kind soul or
it will have to wait until I get the hardware.
sdhci is the only driver I'm aware of that's got (mainlined) support
for start_signal_voltage_switch, are you thinking of any other driver?
You may look at only in tree drivers who have implemented
start_singnal_voltage_switch() ops. Our msm_sdcc* driver has also
implemented it but it's not in tree driver so i may
need to take care of that later once we are synced to kernel version
which will have your patch series.
Yes, SDHCi seeems to be only one in tree driver implemented the
start_singnal_voltage_switch() ops. So you might be good fixing the same.
I'm developing for the MMCI driver, but the UHS support code is still
pending mainlining.
Kind regards, Johan
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