[BUG] mmc_regulator_set_ocr can't cope with regulator-fixed

[Peter Geis]

On Thu, Aug 5, 2021 at 5:59 AM Jaehoon Chung <jh80.chung at samsung.com> wrote:
>
> Hi,
>
> On 8/4/21 11:32 PM, Peter Geis wrote:
> > Good Morning,
> >
> > I've encountered a fun issue with the dw-mmc driver while working on
> > enabling support for the Quartz-64 Model A.
> > The regulator-fixed driver supports enabling via a gpio, but does not
> > have the ops to set voltage as it is fixed.
> > The dw-mmc calls mmc_regulator_set_ocr for vmmc, which attempts to set
> > the voltage first but fails due to the lack of the voltage ops. It
> > then bails returning -EINVAL.
> > This leads to the following message :
> > dwmmc_rockchip fe2b0000.mmc: could not set regulator OCR (-22)
>
> What is vdd value (ocr_avail value) on your target?
> I didn't see its case until now. If there is a real bug, I will try to check again.

What brought this front and center is actually another bug with the
dw-mmc-rk driver (I don't know if it affects other dw-mmc drivers)
vmmc is 3.3v on this board, but with broken-cd set polling causes the
following splat constantly.

[   30.719846] dwmmc_rockchip fe2b0000.mmc: could not set regulator OCR (-22)
[   30.720488] dwmmc_rockchip fe2b0000.mmc: failed to enable vmmc regulator
[   30.763736] dwmmc_rockchip fe2b0000.mmc: could not set regulator OCR (-22)
[   30.764379] dwmmc_rockchip fe2b0000.mmc: failed to enable vmmc regulator
[   30.778231] dwmmc_rockchip fe2b0000.mmc: failed to set rate 300000Hz
[   30.795042] dwmmc_rockchip fe2b0000.mmc: failed to set rate 300000Hz
[   30.798735] dwmmc_rockchip fe2b0000.mmc: failed to set rate 300000Hz
[   30.816591] dwmmc_rockchip fe2b0000.mmc: failed to set rate 300000Hz
[   30.820303] dwmmc_rockchip fe2b0000.mmc: could not set regulator OCR (-22)
[   30.820944] dwmmc_rockchip fe2b0000.mmc: failed to enable vmmc regulator
[   30.834794] dwmmc_rockchip fe2b0000.mmc: failed to set rate 200000Hz
[   30.851606] dwmmc_rockchip fe2b0000.mmc: failed to set rate 200000Hz
[   30.855264] dwmmc_rockchip fe2b0000.mmc: failed to set rate 200000Hz
[   30.873197] dwmmc_rockchip fe2b0000.mmc: failed to set rate 200000Hz
[   30.876908] dwmmc_rockchip fe2b0000.mmc: could not set regulator OCR (-22)
[   30.877549] dwmmc_rockchip fe2b0000.mmc: failed to enable vmmc regulator
[   30.891396] dwmmc_rockchip fe2b0000.mmc: failed to set rate 100000Hz
[   30.911704] dwmmc_rockchip fe2b0000.mmc: failed to set rate 100000Hz
[   30.915586] dwmmc_rockchip fe2b0000.mmc: failed to set rate 100000Hz
[   30.948637] dwmmc_rockchip fe2b0000.mmc: failed to set rate 100000Hz

I looked through the code path and if the OCR voltage is set to the
fixed regulator voltage it should just return success. I think I need
to change that error to output the voltage it tried to set, just to
see if something weird is going on.

Also, I've got a possible fix to the dw-mmc issue, the following patch
changes the behavior to only enable a fixed regulator, not try to set
the voltage. It's a split between the behavior when vmmc isn't defined
at all and when its a variable regulator:

diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
index d333130d1531..b30102980261 100644
--- a/drivers/mmc/host/dw_mmc.c
+++ b/drivers/mmc/host/dw_mmc.c
@@ -1446,11 +1446,13 @@ static void dw_mci_set_ios(struct mmc_host
*mmc, struct mmc_ios *ios)
  switch (ios->power_mode) {
  case MMC_POWER_UP:
  if (!IS_ERR(mmc->supply.vmmc)) {
- ret = mmc_regulator_set_ocr(mmc, mmc->supply.vmmc,
- ios->vdd);
+ if (mmc->ocr_avail > 0)
+ ret = mmc_regulator_set_ocr(mmc, mmc->supply.vmmc, ios->vdd);
+ else
+ ret = regulator_enable(mmc->supply.vmmc);
+
  if (ret) {
- dev_err(slot->host->dev,
- "failed to enable vmmc regulator\n");
+ dev_err(slot->host->dev, "failed to enable vmmc regulator\n");
  /*return, if failed turn on vmmc*/
  return;
  }

>
> Best Regards,
> Jaehoon Chung
>
> >
> > This can be fixed by switching to regulator-gpio for the vmmc supply
> > to the sdmmc controller, however the sdio controller vmmc is provided
> > by a fixed regulator that is always on. Obviously the regulator-gpio
> > isn't an option, as it has no gpio to enable.
> >
> > Removing the vmmc phandle from the sdio node is an option, but then it
> > doesn't fully describe the hardware (it's also a non-standard 4.4v).
> > I had considered changing the check in dw-mmc.c [1] to continue in the
> > case of -EINVAL, but there are other places in the regulator framework
> > that can also return that and it doesn't address the underlying issue.
> >
> > As such I'm reaching out to the experts to see what the best course of
> > action is here.
> > Please weigh in with what you think.
> >
> > Very Respectfully,
> > Peter Geis
> >
>