Re: [RFC PATCH 2/2] mmc: dw_mmc: check card present before starting request

[Shawn Lin]

Hi Jaehoon,

On 2016/5/27 8:53, Jaehoon Chung wrote:
> Hi Shawn,
>
> On 05/26/2016 12:08 PM, Shawn Lin wrote:
> > The main reason to add this check is to avoid unnecessary
> > mmc_request if the card is removed. Although we have already
> > check this in dw_mci_handle_cd for runtime usage of sd card and
> > dw_mci_init_slot for noremovable devices, but there is a timing
> > gap before it really calls dw_mci_get_cd as mmc_detect_change needs
> > some delay here.
>
> What's unnecessary mmc_request?

the on-going read/write/ and the corresponding sbc like cmd13, etc.


> > Another gain here is that we could save some checkings of card status
> > after sd card been removed.
> >
> > Signed-off-by: Shawn Lin <shawn.lin@xxxxxxxxxxxxxx>
> > ---
> >
> >  drivers/mmc/host/dw_mmc.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> > index cb30e91..2940d24 100644
> > --- a/drivers/mmc/host/dw_mmc.c
> > +++ b/drivers/mmc/host/dw_mmc.c
> > @@ -105,6 +105,7 @@ struct idmac_desc {
> >  static bool dw_mci_reset(struct dw_mci *host);
> >  static bool dw_mci_ctrl_reset(struct dw_mci *host, u32 reset);
> >  static int dw_mci_card_busy(struct mmc_host *mmc);
> > +static int dw_mci_get_cd(struct mmc_host *mmc);
> >
> >  #if defined(CONFIG_DEBUG_FS)
> >  static int dw_mci_req_show(struct seq_file *s, void *v)
> > @@ -1248,6 +1249,8 @@ static void dw_mci_request(struct mmc_host *mmc, struct mmc_request *mrq)
> >
> >  	WARN_ON(slot->mrq);
> >
> > +	dw_mci_get_cd(mmc);
> > +
>
> If my understanding is right, it can be replaced
>
> if (!test_bit(DW_MMC_CARD_PRESENT, &slot->flags))
>
> to
>
> if (!dw_mci_get_cd(mmc))

yeah~ It looks better.

> Best Regards,
> Jaehoon Chung
>
>
>
> >  	/*
> >  	 * The check for card presence and queueing of the request must be
> >  	 * atomic, otherwise the card could be removed in between and the


--
Best Regards
Shawn Lin