Re: [PATCH v2] thermal: ti-soc-thermal: dra7: Implement Workaround for Errata i814 - Bandgap Temperature read Dtemp can be corrupted

[Keerthy <a0393675@ti.com>]

On Friday 10 April 2015 12:06 PM, Keerthy wrote:
> Bandgap Temperature read Dtemp can be corrupted
>
> DESCRIPTION
>          Read accesses to registers listed below can be corrupted due to incorrect resynchronization between
>          clock domains.
>
>          Read access to registers below can be corrupted :
>                  • CTRL_CORE_DTEMP_MPU/GPU/CORE/DSPEVE/IVA_n (n = 0 to 4)
>          • CTRL_CORE_TEMP_SENSOR_MPU/GPU/CORE/DSPEVE/IVA_n
>
> WORKAROUND
>          Multiple reads to CTRL_CORE_TEMP_SENSOR_MPU/GPU/CORE/DSPEVE/IVA[9:0]:
>          BGAP_DTEMPMPU/GPU/CORE/DSPEVE/IVA is needed to discard false value and read right value:
>                  1. Perform two successive reads to BGAP_DTEMP bit field.
>                          (a) If read1 returns Val1 and read2 returns Val1, then right value is Val1.
>                          (b) If read1 returns Val1, read 2 returns Val2, a third read is needed.
>                  2. Perform third read
>                          (a) If read3 returns Val2 then right value is Val2.
>                          (b) If read3 returns Val3, then right value is Val3.
>
>          The above in gist means if val1 and val2 are the same then we can go ahead with that value
>          else we need a third read which will be right since synchronization will be complete by then.
>
> Signed-off-by: Keerthy <j-keerthy@ti.com>
> ---

A Gentle ping on this. This has the comments fixed.

>
> Changes in V2:
>
>    * Added more details in the description part.
>    * Indented the comments.
>    * Renamed ti_dra7_bandgap_read_temp to ti_errata814_bandgap_read_temp.
>
>   .../thermal/ti-soc-thermal/dra752-thermal-data.c   |  3 +-
>   drivers/thermal/ti-soc-thermal/ti-bandgap.c        | 37 +++++++++++++++++++++-
>   drivers/thermal/ti-soc-thermal/ti-bandgap.h        |  4 +++
>   3 files changed, 42 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/thermal/ti-soc-thermal/dra752-thermal-data.c b/drivers/thermal/ti-soc-thermal/dra752-thermal-data.c
> index a492927..58b5c66 100644
> --- a/drivers/thermal/ti-soc-thermal/dra752-thermal-data.c
> +++ b/drivers/thermal/ti-soc-thermal/dra752-thermal-data.c
> @@ -420,7 +420,8 @@ const struct ti_bandgap_data dra752_data = {
>   			TI_BANDGAP_FEATURE_FREEZE_BIT |
>   			TI_BANDGAP_FEATURE_TALERT |
>   			TI_BANDGAP_FEATURE_COUNTER_DELAY |
> -			TI_BANDGAP_FEATURE_HISTORY_BUFFER,
> +			TI_BANDGAP_FEATURE_HISTORY_BUFFER |
> +			TI_BANDGAP_FEATURE_ERRATA_814,
>   	.fclock_name = "l3instr_ts_gclk_div",
>   	.div_ck_name = "l3instr_ts_gclk_div",
>   	.conv_table = dra752_adc_to_temp,
> diff --git a/drivers/thermal/ti-soc-thermal/ti-bandgap.c b/drivers/thermal/ti-soc-thermal/ti-bandgap.c
> index 74c0e34..94acd80 100644
> --- a/drivers/thermal/ti-soc-thermal/ti-bandgap.c
> +++ b/drivers/thermal/ti-soc-thermal/ti-bandgap.c
> @@ -119,6 +119,37 @@ exit:
>   }
>
>   /**
> + * ti_errata814_bandgap_read_temp() - helper function to read dra7 sensor temperature
> + * @bgp: pointer to ti_bandgap structure
> + * @reg: desired register (offset) to be read
> + *
> + * Function to read dra7 bandgap sensor temperature. This is done separately
> + * so as to workaround the errata "Bandgap Temperature read Dtemp can be
> + * corrupted" - Errata ID: i814".
> + * Read accesses to registers listed below can be corrupted due to incorrect
> + * resynchronization between clock domains.
> + * Read access to registers below can be corrupted :
> + * CTRL_CORE_DTEMP_MPU/GPU/CORE/DSPEVE/IVA_n (n = 0 to 4)
> + * CTRL_CORE_TEMP_SENSOR_MPU/GPU/CORE/DSPEVE/IVA_n
> + *
> + * Return: the register value.
> + */
> +static u32 ti_errata814_bandgap_read_temp(struct ti_bandgap *bgp,  u32 reg)
> +{
> +	u32 val1, val2;
> +
> +	val1 = ti_bandgap_readl(bgp, reg);
> +	val2 = ti_bandgap_readl(bgp, reg);
> +
> +	/* If both times we read the same value then that is right */
> +	if (val1 == val2)
> +		return val1;
> +
> +	/* if val1 and val2 are different read it third time */
> +	return ti_bandgap_readl(bgp, reg);
> +}
> +
> +/**
>    * ti_bandgap_read_temp() - helper function to read sensor temperature
>    * @bgp: pointer to ti_bandgap structure
>    * @id: bandgap sensor id
> @@ -148,7 +179,11 @@ static u32 ti_bandgap_read_temp(struct ti_bandgap *bgp, int id)
>   	}
>
>   	/* read temperature */
> -	temp = ti_bandgap_readl(bgp, reg);
> +	if (TI_BANDGAP_HAS(bgp, ERRATA_814))
> +		temp = ti_errata814_bandgap_read_temp(bgp, reg);
> +	else
> +		temp = ti_bandgap_readl(bgp, reg);
> +
>   	temp &= tsr->bgap_dtemp_mask;
>
>   	if (TI_BANDGAP_HAS(bgp, FREEZE_BIT))
> diff --git a/drivers/thermal/ti-soc-thermal/ti-bandgap.h b/drivers/thermal/ti-soc-thermal/ti-bandgap.h
> index b3adf72..b2da3fc 100644
> --- a/drivers/thermal/ti-soc-thermal/ti-bandgap.h
> +++ b/drivers/thermal/ti-soc-thermal/ti-bandgap.h
> @@ -318,6 +318,9 @@ struct ti_temp_sensor {
>    * TI_BANDGAP_FEATURE_HISTORY_BUFFER - used when the bandgap device features
>    *	a history buffer of temperatures.
>    *
> + * TI_BANDGAP_FEATURE_ERRATA_814 - used to workaorund when the bandgap device
> + *	has Errata 814
> + *
>    * TI_BANDGAP_HAS(b, f) - macro to check if a bandgap device is capable of a
>    *      specific feature (above) or not. Return non-zero, if yes.
>    */
> @@ -331,6 +334,7 @@ struct ti_temp_sensor {
>   #define TI_BANDGAP_FEATURE_FREEZE_BIT		BIT(7)
>   #define TI_BANDGAP_FEATURE_COUNTER_DELAY	BIT(8)
>   #define TI_BANDGAP_FEATURE_HISTORY_BUFFER	BIT(9)
> +#define TI_BANDGAP_FEATURE_ERRATA_814		BIT(10)
>   #define TI_BANDGAP_HAS(b, f)			\
>   			((b)->conf->features & TI_BANDGAP_FEATURE_ ## f)
>
>