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

[Ulf Hansson]

On Mon, 10 Dec 2018 at 14:23, Faiz Abbas <faiz_abbas@xxxxxx> wrote:
>
> Hi Uffe,
>
> On 05/12/18 7:20 PM, Ulf Hansson wrote:
> > 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?
>
> There are no plans to support runtime_suspend()/resume() any time in the
> near future. If its ok with you, I would like to get this patch in
> without any changes. We can change it in case a need for
> runtime_suspend()/_resume() does arise.

Right, I am okay with that. Due to recent changes to sdhci-omap
$subject patch doesn't apply, can you please rebase!?

Additionally, I realized that we should fold in patch updating the DT
doc for sdhci-omap, adding the property for the thermal zone. I
regards to that, I am wondering if "cpu_thermal", is really the
correct name of the zone. The point is, I am guessing the zone could
change along with the SoCs/platforms.

Kind regards
Uffe