RE: [PATCH] mmc: sd: UHS-I bus speed should be set last in UHS initialization

Subhash Jadavani
2011-08-02T09:12:47Z

Hi Arindam,

Thank you for the review. Please find few comments inline.

> -----Original Message-----
> From: Nath, Arindam [mailto:Arindam.Nath@amd.com]
> Sent: Tuesday, August 02, 2011 12:38 PM
> To: Chris Ball; Subhash Jadavani
> Cc: linux-mmc@vger.kernel.org; linux-arm-msm@vger.kernel.org; Philip
> Rakity; zhangfei gao
> Subject: RE: [PATCH] mmc: sd: UHS-I bus speed should be set last in UHS
> initialization
>
> Hi Subhash,
>
>
> > -----Original Message-----
> > From: Chris Ball [mailto:cjb@laptop.org]
> > Sent: Tuesday, August 02, 2011 1:40 AM
> > To: Subhash Jadavani
> > Cc: linux-mmc@vger.kernel.org; linux-arm-msm@vger.kernel.org; Nath,
> > Arindam
> > Subject: Re: [PATCH] mmc: sd: UHS-I bus speed should be set last in
> UHS
> > initialization
> >
> > Hi Subhash, adding Arindam for review,
> >
> > On Mon, Aug 01 2011, Subhash Jadavani wrote:
> > > mmc_sd_init_uhs_card function sets the driver type, current limit
> > > and bus speed mode on card as well as on host controller side.
> > >
> > > Currently bus speed mode is set by sending CMD6 to card and
> > > immediately setting the timing mode in host controller. But
> > > then before initiating tuning sequence, it also tries to set
> > > current limit by sending CMD6 to card which results in data
> > > timeout errors in controller if bus speed mode is SDR50/SDR104
> mode.
> > >
> > > So basically bus speed mode should be set only after current limit
> > > is set in the card and immediately after setting the bus speed
> mode,
> > > tuning sequence should be initiated.
> > >
> > > Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
> > > ---
> > > drivers/mmc/core/sd.c | 57 ++++++++++++++++++++++++++++++++-----
> --
> > ---------
> > > 1 files changed, 38 insertions(+), 19 deletions(-)
> > >
> > > diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> > > index ff27741..d257496 100644
> > > --- a/drivers/mmc/core/sd.c
> > > +++ b/drivers/mmc/core/sd.c
> > > @@ -459,10 +459,9 @@ static int sd_select_driver_type(struct
> mmc_card
> > *card, u8 *status)
> > > return 0;
> > > }
> > >
> > > -static int sd_set_bus_speed_mode(struct mmc_card *card, u8
> *status)
> > > +static int sd_get_bus_speed_mode(struct mmc_card *card)
> > > {
> > > - unsigned int bus_speed = 0, timing = 0;
> > > - int err;
> > > + int bus_speed = 0;
> > >
> > > /*
> > > * If the host doesn't support any of the UHS-I modes, fallback
> > on
> > > @@ -470,37 +469,56 @@ static int sd_set_bus_speed_mode(struct
> > mmc_card *card, u8 *status)
> > > */
> > > if (!(card->host->caps & (MMC_CAP_UHS_SDR12 | MMC_CAP_UHS_SDR25 |
> > > MMC_CAP_UHS_SDR50 | MMC_CAP_UHS_SDR104 | MMC_CAP_UHS_DDR50)))
> > > - return 0;
> > > + return -EINVAL;
>
> We should not return -EINVAL here, because this is not an error
> condition. This would simply mean that the card and host controller
> will fall back to using the default bus speed, and should still be
> operable. Check the comment below too.

Return value of this function gets used in sd_set_bus_speed_mode() function
and compared against all the valid bus speed modes. If we choose to return 0
from here then '0' corresponds to valid bus speed mode
'UHS_SDR12_BUS_SPEED'.

#define UHS_SDR12_BUS_SPEED 0
#define UHS_SDR25_BUS_SPEED 1
#define UHS_SDR50_BUS_SPEED 2
#define UHS_SDR104_BUS_SPEED 3
#define UHS_DDR50_BUS_SPEED 4

If we don't want to return the error value from this function then we can
basically remove following check from this *get* function and move it to
each *set* function before calling *get*. Please see more comments inline in
*set* functions below.

if (!(card->host->caps & (MMC_CAP_UHS_SDR12 | MMC_CAP_UHS_SDR25 |
MMC_CAP_UHS_SDR50 | MMC_CAP_UHS_SDR104 | MMC_CAP_UHS_DDR50)))
return -EINVAL;

>
> > >
> > > if ((card->host->caps & MMC_CAP_UHS_SDR104) &&
> > > (card->sw_caps.sd3_bus_mode & SD_MODE_UHS_SDR104)) {
> > > bus_speed = UHS_SDR104_BUS_SPEED;
> > > - timing = MMC_TIMING_UHS_SDR104;
> > > - card->sw_caps.uhs_max_dtr = UHS_SDR104_MAX_DTR;
> > > } else if ((card->host->caps & MMC_CAP_UHS_DDR50) &&
> > > (card->sw_caps.sd3_bus_mode & SD_MODE_UHS_DDR50)) {
> > > bus_speed = UHS_DDR50_BUS_SPEED;
> > > - timing = MMC_TIMING_UHS_DDR50;
> > > - card->sw_caps.uhs_max_dtr = UHS_DDR50_MAX_DTR;
> > > } else if ((card->host->caps & (MMC_CAP_UHS_SDR104 |
> > > MMC_CAP_UHS_SDR50)) && (card->sw_caps.sd3_bus_mode &
> > > SD_MODE_UHS_SDR50)) {
> > > bus_speed = UHS_SDR50_BUS_SPEED;
> > > - timing = MMC_TIMING_UHS_SDR50;
> > > - card->sw_caps.uhs_max_dtr = UHS_SDR50_MAX_DTR;
> > > } else if ((card->host->caps & (MMC_CAP_UHS_SDR104 |
> > > MMC_CAP_UHS_SDR50 | MMC_CAP_UHS_SDR25)) &&
> > > (card->sw_caps.sd3_bus_mode & SD_MODE_UHS_SDR25)) {
> > > bus_speed = UHS_SDR25_BUS_SPEED;
> > > - timing = MMC_TIMING_UHS_SDR25;
> > > - card->sw_caps.uhs_max_dtr = UHS_SDR25_MAX_DTR;
> > > } else if ((card->host->caps & (MMC_CAP_UHS_SDR104 |
> > > MMC_CAP_UHS_SDR50 | MMC_CAP_UHS_SDR25 |
> > > MMC_CAP_UHS_SDR12)) && (card->sw_caps.sd3_bus_mode &
> > > SD_MODE_UHS_SDR12)) {
> > > bus_speed = UHS_SDR12_BUS_SPEED;
> > > + }
> > > +
> > > + return bus_speed;
> > > +}
> > > +
> > > +static int sd_set_bus_speed_mode(struct mmc_card *card, u8
> *status)
> > > +{
> > > + int err, bus_speed;
> > > + unsigned int timing = 0;
> > > +

We need add this check here.

if (!(card->host->caps & (MMC_CAP_UHS_SDR12 | MMC_CAP_UHS_SDR25 |
MMC_CAP_UHS_SDR50 | MMC_CAP_UHS_SDR104 |
MMC_CAP_UHS_DDR50)))
return 0;

> > > + bus_speed = sd_get_bus_speed_mode(card);
> > > +
> > > + if (bus_speed == UHS_SDR104_BUS_SPEED) {
> > > + timing = MMC_TIMING_UHS_SDR104;
> > > + card->sw_caps.uhs_max_dtr = UHS_SDR104_MAX_DTR;
> > > + } else if (bus_speed == UHS_DDR50_BUS_SPEED) {
> > > + timing = MMC_TIMING_UHS_DDR50;
> > > + card->sw_caps.uhs_max_dtr = UHS_DDR50_MAX_DTR;
> > > + } else if (bus_speed == UHS_SDR50_BUS_SPEED) {
> > > + timing = MMC_TIMING_UHS_SDR50;
> > > + card->sw_caps.uhs_max_dtr = UHS_SDR50_MAX_DTR;
> > > + } else if (bus_speed == UHS_SDR25_BUS_SPEED) {
> > > + timing = MMC_TIMING_UHS_SDR25;
> > > + card->sw_caps.uhs_max_dtr = UHS_SDR25_MAX_DTR;
> > > + } else if (bus_speed == UHS_SDR12_BUS_SPEED) {
> > > timing = MMC_TIMING_UHS_SDR12;
> > > card->sw_caps.uhs_max_dtr = UHS_SDR12_MAX_DTR;
> > > + } else {
> > > + return -EINVAL;
> > > }
> >
> > Minor change: I think "switch (sd_get_bus_speed_mode(card))" would be
> > cleaner.

Yes, we can replace it with switch. I will do it next patch rev.

> >
> > >
> > > card->sd_bus_speed = bus_speed;
> > > @@ -522,6 +540,7 @@ static int sd_set_bus_speed_mode(struct
> mmc_card
> > *card, u8 *status)
> > > static int sd_set_current_limit(struct mmc_card *card, u8 *status)
> > > {
> > > int current_limit = 0;
> > > + unsigned int bus_speed = sd_get_bus_speed_mode(card);
> > > int err;

We need add this check here.

if (!(card->host->caps & (MMC_CAP_UHS_SDR12 | MMC_CAP_UHS_SDR25 |
MMC_CAP_UHS_SDR50 | MMC_CAP_UHS_SDR104 |
MMC_CAP_UHS_DDR50)))
return 0;

> > >
> > > /*
> > > @@ -529,9 +548,9 @@ static int sd_set_current_limit(struct mmc_card
> > *card, u8 *status)
> > > * bus speed modes. For other bus speed modes, we set the default
> > > * current limit of 200mA.
> > > */
> > > - if ((card->sd_bus_speed == UHS_SDR50_BUS_SPEED) ||
> > > - (card->sd_bus_speed == UHS_SDR104_BUS_SPEED) ||
> > > - (card->sd_bus_speed == UHS_DDR50_BUS_SPEED)) {
> > > + if ((bus_speed == UHS_SDR50_BUS_SPEED) ||
> > > + (bus_speed == UHS_SDR104_BUS_SPEED) ||
> > > + (bus_speed == UHS_DDR50_BUS_SPEED)) {
> > > if (card->host->caps & MMC_CAP_MAX_CURRENT_800) {
> > > if (card->sw_caps.sd3_curr_limit &
> > SD_MAX_CURRENT_800)
> > > current_limit = SD_SET_CURRENT_LIMIT_800;
> > > @@ -613,13 +632,13 @@ static int mmc_sd_init_uhs_card(struct
> mmc_card
> > *card)
> > > if (err)
> > > goto out;
> > >
> > > - /* Set bus speed mode of the card */
> > > - err = sd_set_bus_speed_mode(card, status);
> > > + /* Set current limit for the card */
> > > + err = sd_set_current_limit(card, status);
> > > if (err)
> > > goto out;
> > >
> > > - /* Set current limit for the card */
> > > - err = sd_set_current_limit(card, status);
> > > + /* Set bus speed mode of the card */
> > > + err = sd_set_bus_speed_mode(card, status);
>
> Now supposing that we return -EINVAL here, then that would imply that
> mmc_sd_init_uhs_card() failed, but that should not be the case. Like I
> mentioned before, the card should still be operable using default speed
> mode.

When you say Default speed mode, does it mean SDR12 mode?

Thanks,
Subhash

>
> Thanks,
> Arindam
>
> > > if (err)
> > > goto out;
> > >
> >
> > Thanks,
> >
> > - Chris.
> > --
> > Chris Ball <cjb@laptop.org> <http://printf.net/>
> > One Laptop Per Child
>