Re: [PATCH V1 07/11] mmc: cqhci: add quirk for setting DCMD CMD_TIMING

[Ritesh Harjani]

On 3/6/2019 6:30 PM, Adrian Hunter wrote:
> On 2/03/19 7:20 AM, Sowjanya Komatineni wrote:
> > This patch adds a quirk for setting CMD_TIMING to 1 in descriptor
> > for DCMD with R1B response type to allow the command to be sent to
> > device during data activity or busy time.
> >
> > Tegra186 CQHCI host has bug where it selects DATA_PRESENT_SELECT
> > to 1 by CQHCI controller for DCMDs with R1B response type and
> > since DCMD does not trigger any data transfer, DCMD task complete
> > happens leaving the DATA FSM of host controller in wait state for
> > data.
> >
> > This effects the data transfer task issued after R1B DCMD task
> > and no interrupt is generated for the data transfer task.
> >
> > SW WAR for this issue is to set CMD_TIMING bit to 1 in DCMD task
> > descriptor and as DCMD task descriptor preparation is done by
> > cqhci driver, this patch adds cqequirk to handle this.
> >
> > Signed-off-by: Sowjanya Komatineni <skomatineni@xxxxxxxxxx>
> > ---
> >   drivers/mmc/host/cqhci.c | 5 ++++-
> >   drivers/mmc/host/cqhci.h | 1 +
> >   2 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/host/cqhci.c b/drivers/mmc/host/cqhci.c
> > index a8af682a9182..b34c07125f32 100644
> > --- a/drivers/mmc/host/cqhci.c
> > +++ b/drivers/mmc/host/cqhci.c
> > @@ -521,7 +521,10 @@ static void cqhci_prep_dcmd_desc(struct mmc_host *mmc,
> >   	} else {
> >   		if (mrq->cmd->flags & MMC_RSP_R1B) {
> >   			resp_type = 0x3;
> > -			timing = 0x0;
> > +			if (cq_host->quirks & CQHCI_QUIRK_CMD_TIMING_R1B_DCMD)
> > +				timing = 0x1;
> > +			else
> > +				timing = 0x0;
> I was thinking it would be nice if there was a generic way for drivers to
> make changes to descriptors before a task is started.  Currently there is
> host->ops->write_l() which would make it possible by checking for CQHCI_TDBR
> register and, in this case, the DCMD tag.  We would need to export
> get_desc(), perhaps rename it cqhci_get_desc() and put it in cqhci.h since
> it is an inline function.

We take spin_lock_irqsave after the descriptor is prepared and before 
writing to TDBR.
Not sure but tomorrow this may become a limitation for drivers to make 
changes to
descriptors if they edit descriptors in host->ops->write_l() call.
Though in this case it is not required here.

> Alternatively we could add host->ops for descriptor preparation.

Both ways sounds good to me.
But maybe adding a host->ops for descriptor preparation is better way to go,
since that will be the right interface exposed to make changes to 
descriptors.

> What do people think?
>
> >   		} else {
> >   			resp_type = 0x2;
> >   			timing = 0x1;
> > diff --git a/drivers/mmc/host/cqhci.h b/drivers/mmc/host/cqhci.h
> > index 9e68286a07b4..f96d8565cc07 100644
> > --- a/drivers/mmc/host/cqhci.h
> > +++ b/drivers/mmc/host/cqhci.h
> > @@ -170,6 +170,7 @@ struct cqhci_host {
> >   
> >   	u32 quirks;
> >   #define CQHCI_QUIRK_SHORT_TXFR_DESC_SZ	0x1
> > +#define CQHCI_QUIRK_CMD_TIMING_R1B_DCMD	0x2
> >   
> >   	bool enabled;
> >   	bool halted;