RE: [PATCH 02/12] mmc: sd: add support for signal voltage switch procedure

Nath, Arindam
2011-03-03T13:35:42Z

Hi Subhash,

> -----Original Message-----
> From: subhashj@codeaurora.org [mailto:subhashj@codeaurora.org]
> Sent: Thursday, March 03, 2011 6:46 PM
> To: Nath, Arindam; cjb@laptop.org
> Cc: linux-mmc@vger.kernel.org; Su, Henry; Lu, Aaron;
> anath.amd@gmail.com
> Subject: RE: [PATCH 02/12] mmc: sd: add support for signal voltage
> switch procedure
>
>
>
> > -----Original Message-----
> > From: linux-mmc-owner@vger.kernel.org [mailto:linux-mmc-
> > owner@vger.kernel.org] On Behalf Of Nath, Arindam
> > Sent: Wednesday, March 02, 2011 1:36 PM
> > To: subhashj@codeaurora.org; cjb@laptop.org
> > Cc: linux-mmc@vger.kernel.org; Su, Henry; Lu, Aaron;
> > anath.amd@gmail.com
> > Subject: RE: [PATCH 02/12] mmc: sd: add support for signal voltage
> > switch procedure
> >
> > Hi Subhash,
> >
> >
> > > -----Original Message-----
> > > From: subhashj@codeaurora.org [mailto:subhashj@codeaurora.org]
> > > Sent: Tuesday, March 01, 2011 9:33 PM
> > > To: Nath, Arindam; cjb@laptop.org
> > > Cc: linux-mmc@vger.kernel.org; Su, Henry; Lu, Aaron;
> > > anath.amd@gmail.com
> > > Subject: RE: [PATCH 02/12] mmc: sd: add support for signal voltage
> > > switch procedure
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: linux-mmc-owner@vger.kernel.org [mailto:linux-mmc-
> > > > owner@vger.kernel.org] On Behalf Of Arindam Nath
> > > > Sent: Tuesday, February 15, 2011 3:05 PM
> > > > To: cjb@laptop.org
> > > > Cc: linux-mmc@vger.kernel.org; henry.su@amd.com;
> aaron.lu@amd.com;
> > > > anath.amd@gmail.com; Arindam Nath
> > > > Subject: [PATCH 02/12] mmc: sd: add support for signal voltage
> > switch
> > > > procedure
> > > >
> > > > Host Controller v3.00 adds another Capabilities register. We can
> > > > directly read this register without any version checking since
> the
> > > > new register bits will be considred as reserved in older
> > controllers,
> > > > and will be read as 0. Apart from other things, this new register
> > > > indicates whether the Host Controller supports SDR50, SDR104, and
> > > > DDR50 UHS-I modes. So depending on the host support, we set
> > > > the corresponding MMC_CAP_* flags. One more new register. Host
> > > Control2
> > > > is added in v3.00, which is used during Signal Voltage Switch
> > > prcedure
> > > > described below.
> > > >
> > > > Since as per v3.00 spec, UHS-I supported hosts should set S18R to
> > 1,
> > > > we set S18R (bit 24) of OCR before sending ACMD41. We also need
> to
> > > set
> > > > XPC (bit 28) of OCR in case the host can supply >150mA. This
> > support
> > > is
> > > > indicated by the Maximum Current Capabilities register of the
> Host
> > > > Controller.
> > > >
> > > > If the response of ACMD41 has both CCS and S18A set, we start the
> > > > signal voltage switch procedure, which if successfull, will
> switch
> > > > the card from 3.3V signalling to 1.8V signalling. Signal voltage
> > > > switch procedure adds support for a new command CMD11 in the
> > Physical
> > > > Layer Spec v3.01. As part of this procedure, we need to set 1.8V
> > > > Signalling
> > > > Enable (bit 3) of Host Control2 register, which if remains set
> > after
> > > > 5ms,
> > > > means the switch to 1.8V signalling is successfull. Otherwise, we
> > > clear
> > > > bit 24 of OCR and retry the initialization sequence.
> > > >
> > > > Signed-off-by: Arindam Nath <arindam.nath@amd.com>
> > > > ---
> > > > drivers/mmc/core/sd.c | 37 ++++++++++-
> > > > drivers/mmc/core/sd_ops.c | 25 ++++++++
> > > > drivers/mmc/core/sd_ops.h | 1 +
> > > > drivers/mmc/host/sdhci.c | 147
> > > > +++++++++++++++++++++++++++++++++++++++++----
> > > > drivers/mmc/host/sdhci.h | 18 +++++-
> > > > include/linux/mmc/host.h | 8 +++
> > > > include/linux/mmc/sd.h | 1 +
> > > > 7 files changed, 219 insertions(+), 18 deletions(-)
> > > >
> > > > diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c
> > > > index b3f8a3c..e968d5c 100644
> > > > --- a/drivers/mmc/core/sd.c
> > > > +++ b/drivers/mmc/core/sd.c
> > > > @@ -408,6 +408,7 @@ struct device_type sd_type = {
> > > > int mmc_sd_get_cid(struct mmc_host *host, u32 ocr, u32 *cid)
> > > > {
> > > > int err;
> > > > + u32 rocr;
> > > >
> > > > /*
> > > > * Since we're changing the OCR value, we seem to
> > > > @@ -427,10 +428,25 @@ int mmc_sd_get_cid(struct mmc_host *host,
> u32
> > > > ocr, u32 *cid)
> > > > if (!err)
> > > > ocr |= 1 << 30;
> > > >
> > > > - err = mmc_send_app_op_cond(host, ocr, NULL);
> > > > + /* If the host can supply more than 150mA, XPC should be set
> to
> > > > 1. */
> > > > + if (host->caps & (MMC_CAP_SET_XPC_330 | MMC_CAP_SET_XPC_300 |
> > > > + MMC_CAP_SET_XPC_180))
> > > > + ocr |= 1 << 28;
> > > > +
> > >
> > > Why do you need MMC_CAP_SET_XPC_300 here? MMC_CAP_SET_XPC_330 &
> > > MMC_CAP_SET_XPC_180 is not enough?
> >
> > According to the Host Controller Spec v3.00, section 2.2.26:
> >
> > "If a Host System can afford more than 150mA, Host Driver set XPC to
> > 1."
> >
> > Now since >150mA can be set for 1.8V, 3.0V and 3.3V, the above
> > condition checks for all these cases.
> >
>
> 3.0v and 3.3v is part of High voltage range supported by card (2.7v-
> 3.3v).
> Now if host supports any voltage from this range with 150ma driver
> strength
> then I think only config say MMC_CAP_SET_XPC_HV (high voltage) should
> be set
> by
> host and then only one check required here. Does it make sense?

You have a valid point here. But I kept the configs *XPC_300 and *XPC_330 separate so that in future if someone wants to base his/her code on either of the flags being set, but not both, they can easily do so. If you still think it is a good idea to have a common *CAP for both of them, please let me know. I will modify the code accordingly.

Thanks,
Arindam