linux-kernel - Re: [PATCH] mmc: rtsx_pci_sdmmc: implement sdmmc_card

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Message-ID: <CAPDyKFpt_7SgXKEqpGSYYNcdhrNYLsYEKM0N=sG7YeVxVaYzfg@mail.gmail.com>
Date: Wed, 21 Jan 2026 15:54:10 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Ricky WU <ricky_wu@...ltek.com>, Matthew Schwartz <matthew.schwartz@...ux.dev>
Cc: "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: rtsx_pci_sdmmc: implement sdmmc_card_busy function

On Thu, 15 Jan 2026 at 11:23, Ricky WU <ricky_wu@...ltek.com> wrote:
>
> Hi Matthew,
>
> Thanks for working on this patch.
>
> We’ve tested this change on our platforms and can confirm that adding the
> card_busy() callback does resolve the
> “cannot verify signal voltage switch” issue for us 👍.
>
> That said, while reviewing the change we noticed a potential redundancy in
> the existing driver logic. In sdmmc_switch_voltage() we already perform
> explicit DAT line stabilization checks via
> sd_wait_voltage_stable_1() and sd_wait_voltage_stable_2().
>
> Once card_busy() is implemented and used by the MMC core during the
> voltage-switch verification phase, these two stabilization steps appear to
> be partially overlapping with what the core now validates via
> card_busy(). In our testing, with card_busy() present, the stable_1 /
> stable_2 logic no longer seems strictly necessary and could likely be
> simplified or removed with some adjustment.
>
> From a process point of view, we’re not sure which approach you’d prefer:
>
> Land your patch as-is first, and then we can follow up with a separate
> cleanup/modification patch to adjust sdmmc_switch_voltage(), or
>
> We can prepare an additional patch that builds on top of yours and share
> it with you for review, so the changes can be aligned together.
>
> Please let us know which option you think makes more sense for upstream, or
> if you’d prefer a different approach.
>
> Thanks again for the fix and for looking into this driver.
>
> Best regards,
> Ricky
>
> > rtsx_pci_sdmmc does not have an sdmmc_card_busy function, so any voltage
> > switches cause a kernel warning, "mmc0: cannot verify signal voltage switch."
> >
> > Copy the sdmmc_card_busy function from rtsx_pci_usb to rtsx_pci_sdmmc to
> > fix this.
> >
> > Fixes: ff984e57d36e ("mmc: Add realtek pcie sdmmc host driver")
> > Signed-off-by: Matthew Schwartz <matthew.schwartz@...ux.dev>

I have applied this for fixes and by adding a stable tag. I am also
adding Ricky's reviewed/tested-by tag, according to the above.

Let's deal with the potential improvement on-top, as agreed.

Kind regards
Uffe


> > ---
> >  drivers/mmc/host/rtsx_pci_sdmmc.c | 41
> > +++++++++++++++++++++++++++++++
> >  1 file changed, 41 insertions(+)
> >
> > diff --git a/drivers/mmc/host/rtsx_pci_sdmmc.c
> > b/drivers/mmc/host/rtsx_pci_sdmmc.c
> > index dc2587ff8519..4db3328f46df 100644
> > --- a/drivers/mmc/host/rtsx_pci_sdmmc.c
> > +++ b/drivers/mmc/host/rtsx_pci_sdmmc.c
> > @@ -1306,6 +1306,46 @@ static int sdmmc_switch_voltage(struct mmc_host
> > *mmc, struct mmc_ios *ios)
> >         return err;
> >  }
> >
> > +static int sdmmc_card_busy(struct mmc_host *mmc) {
> > +       struct realtek_pci_sdmmc *host = mmc_priv(mmc);
> > +       struct rtsx_pcr *pcr = host->pcr;
> > +       int err;
> > +       u8 stat;
> > +       u8 mask = SD_DAT3_STATUS | SD_DAT2_STATUS | SD_DAT1_STATUS
> > +       | SD_DAT0_STATUS;
> > +
> > +       mutex_lock(&pcr->pcr_mutex);
> > +
> > +       rtsx_pci_start_run(pcr);
> > +
> > +       err = rtsx_pci_write_register(pcr, SD_BUS_STAT,
> > +                                     SD_CLK_TOGGLE_EN |
> > SD_CLK_FORCE_STOP,
> > +                              SD_CLK_TOGGLE_EN);
> > +       if (err)
> > +               goto out;
> > +
> > +       mdelay(1);
> > +
> > +       err = rtsx_pci_read_register(pcr, SD_BUS_STAT, &stat);
> > +       if (err)
> > +               goto out;
> > +
> > +       err = rtsx_pci_write_register(pcr, SD_BUS_STAT,
> > +                                     SD_CLK_TOGGLE_EN |
> > +SD_CLK_FORCE_STOP, 0);
> > +out:
> > +       mutex_unlock(&pcr->pcr_mutex);
> > +
> > +       if (err)
> > +               return err;
> > +
> > +       /* check if any pin between dat[0:3] is low */
> > +       if ((stat & mask) != mask)
> > +               return 1;
> > +       else
> > +               return 0;
> > +}
> > +
> >  static int sdmmc_execute_tuning(struct mmc_host *mmc, u32 opcode)  {
> >         struct realtek_pci_sdmmc *host = mmc_priv(mmc); @@ -1418,6
> > +1458,7 @@ static const struct mmc_host_ops realtek_pci_sdmmc_ops = {
> >         .get_ro = sdmmc_get_ro,
> >         .get_cd = sdmmc_get_cd,
> >         .start_signal_voltage_switch = sdmmc_switch_voltage,
> > +       .card_busy = sdmmc_card_busy,
> >         .execute_tuning = sdmmc_execute_tuning,
> >         .init_sd_express = sdmmc_init_sd_express,  };
> > --
> > 2.52.0
>