Re: [PATCH V1] mmc: sdhci-msm: Avoid early clock doubling during HS400 transition

[Sarthak Garg]

On 11/10/2025 8:09 PM, Bjorn Andersson wrote:
> On Mon, Nov 10, 2025 at 12:08:01PM +0530, Sarthak Garg wrote:
> > According to the hardware programming guide, the clock frequency must
> > remain below 52MHz during the transition to HS400 mode.
> >
> > However,in the current implementation, the timing is set to HS400 (a
> > DDR mode) before adjusting the clock. This causes the clock to double
> > prematurely to 104MHz during the transition phase, violating the
> > specification and potentially resulting in CRC errors or CMD timeouts.
> >
> > This change ensures that clock doubling is avoided during intermediate
> > transitions and is applied only when the card requires a 200MHz clock
> > for HS400 operation.
> >
> > Signed-off-by: Sarthak Garg <sarthak.garg@xxxxxxxxxxxxxxxx>
> > ---
> >   drivers/mmc/host/sdhci-msm.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/host/sdhci-msm.c b/drivers/mmc/host/sdhci-msm.c
> > index 4e5edbf2fc9b..eca6a09a4547 100644
> > --- a/drivers/mmc/host/sdhci-msm.c
> > +++ b/drivers/mmc/host/sdhci-msm.c
> > @@ -355,7 +355,8 @@ static unsigned int msm_get_clock_mult_for_bus_mode(struct sdhci_host *host)
> >   	 */
> >   	if (ios.timing == MMC_TIMING_UHS_DDR50 ||
> >   	    ios.timing == MMC_TIMING_MMC_DDR52 ||
> > -	    ios.timing == MMC_TIMING_MMC_HS400 ||
> > +	    (ios.timing == MMC_TIMING_MMC_HS400 &&
> > +	    ios.clock == MMC_HS200_MAX_DTR) ||
> It's a bit ugly that sdhci_msm_execute_tuning() passes ios.clock as an
> argument to msm_set_clock_rate_for_bus_mode(), which then calls
> msm_get_clock_mult_for_bus_mode() where you reach back into ios.clock.
>
> In fact, having msm_get_clock_mult_for_bus_mode() reach into
> host->mmc->ios to get ios.timing, seems a violation of the original
> intent of the prototype.
>
>
> How about cleaning this up and passing "timing" as an argument to
> msm_set_clock_rate_for_bus_mode(), and then pass host, clock, and timing
> to msm_get_clock_mult_for_bus_mode()?
>
> That way we avoid this mix of passing parameters to the functions in
> both arguments and in state at the same time.
>
> Regards,
> Bjorn


Sure will update in V2.

Regards,
Sarthak


> >   	    host->flags & SDHCI_HS400_TUNING)
> >   		return 2;
> >   	return 1;
> > --
> > 2.34.1