Re: [PATCH] mmc: sdhci-omap: Workaround errata regarding SDR104/HS200 tuning failures (i929)

[Ulf Hansson]

On Fri, 30 Nov 2018 at 06:53, Faiz Abbas <faiz_abbas@xxxxxx> wrote:
>
> Hi Kishon,
>
> On 30/11/18 10:10 AM, Kishon Vijay Abraham I wrote:
> > Hi Faiz,
> >
> > On 30/11/18 12:35 AM, Faiz Abbas wrote:
> >> Errata i929 in certain OMAP5/DRA7XX/AM57XX silicon revisions
> >> (SPRZ426D - November 2014 - Revised February 2018 [1]) mentions
> >> unexpected tuning pattern errors. A small failure band may be present
> >> in the tuning range which may be missed by the current algorithm.
> >> Furthermore, the failure bands vary with temperature leading to
> >> different optimum tuning values for different temperatures.
> >>
> >> As suggested in the related Application Report (SPRACA9B - October 2017
> >> - Revised July 2018 [2]), tuning should be done in two stages.
> >> In stage 1, assign the optimum ratio in the maximum pass window for the
> >> current temperature. In stage 2, if the chosen value is close to the
> >> small failure band, move away from it in the appropriate direction.
> >>
> >> References:
> >> [1] http://www.ti.com/lit/pdf/sprz426
> >> [2] http://www.ti.com/lit/pdf/SPRACA9
> >>
> >> Signed-off-by: Faiz Abbas <faiz_abbas@xxxxxx>
> >> ---
> >>  drivers/mmc/host/Kconfig      |  2 +
> >>  drivers/mmc/host/sdhci-omap.c | 90 ++++++++++++++++++++++++++++++++++-
> >>  2 files changed, 91 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
> >> index 1b58739d9744..6d3553f06f27 100644
> >> --- a/drivers/mmc/host/Kconfig
> >> +++ b/drivers/mmc/host/Kconfig
> >> @@ -969,6 +969,8 @@ config MMC_SDHCI_XENON
> >>  config MMC_SDHCI_OMAP
> >>      tristate "TI SDHCI Controller Support"
> >>      depends on MMC_SDHCI_PLTFM && OF
> >> +    select THERMAL
> >> +    select TI_SOC_THERMAL
> >>      help
> >>        This selects the Secure Digital Host Controller Interface (SDHCI)
> >>        support present in TI's DRA7 SOCs. The controller supports
> >> diff --git a/drivers/mmc/host/sdhci-omap.c b/drivers/mmc/host/sdhci-omap.c
> >> index b3cb39d0db6f..9ccce7ef3a60 100644
> >> --- a/drivers/mmc/host/sdhci-omap.c
> >> +++ b/drivers/mmc/host/sdhci-omap.c
> >> @@ -27,6 +27,7 @@
> >>  #include <linux/regulator/consumer.h>
> >>  #include <linux/pinctrl/consumer.h>
> >>  #include <linux/sys_soc.h>
> >> +#include <linux/thermal.h>
> >>
> >>  #include "sdhci-pltfm.h"
> >>
> >> @@ -286,14 +287,18 @@ static int sdhci_omap_execute_tuning(struct mmc_host *mmc, u32 opcode)
> >>      struct sdhci_host *host = mmc_priv(mmc);
> >>      struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> >>      struct sdhci_omap_host *omap_host = sdhci_pltfm_priv(pltfm_host);
> >> +    struct thermal_zone_device *thermal_dev;
> >>      struct device *dev = omap_host->dev;
> >>      struct mmc_ios *ios = &mmc->ios;
> >>      u32 start_window = 0, max_window = 0;
> >> +    bool single_point_failure = false;
> >>      u8 cur_match, prev_match = 0;
> >>      u32 length = 0, max_len = 0;
> >>      u32 phase_delay = 0;
> >> +    int temperature;
> >>      int ret = 0;
> >>      u32 reg;
> >> +    int i;
> >>
> >>      /* clock tuning is not needed for upto 52MHz */
> >>      if (ios->clock <= 52000000)
> >> @@ -303,6 +308,16 @@ static int sdhci_omap_execute_tuning(struct mmc_host *mmc, u32 opcode)
> >>      if (ios->timing == MMC_TIMING_UHS_SDR50 && !(reg & CAPA2_TSDR50))
> >>              return 0;
> >>
> >> +    thermal_dev = thermal_zone_get_zone_by_name("cpu_thermal");
> >> +    if (IS_ERR(thermal_dev)) {
> >> +            dev_err(dev, "Unable to get thermal zone for tuning\n");
> >> +            return PTR_ERR(thermal_dev);
> >> +    }
> >
> > Can't we get thermal zone once during probe?
> >
>
> Tuning is also (ideally) supposed to happen only once per enumeration.
> Also it doesn't make sense to get a thermal zone for lower speed systems
> that won't do tuning.

Currently sdhci-omap calls pm_runtime_get_sync() during probe, and
then keeps the host device runtime resumed until ->remove() is called
on it. I assume you are going to change that, at some point!?

In other words, what will happen to the host device when it becomes
runtime suspended? Is re-tuning needed when it gets runtime resumed,
which is the case for many other sdhci variants?

Depending on the answer, you may want to fetch the thermal zone during
probe. :-)

Kind regards
Uffe