[PATCH v2] mmc: fsl_esdhc_imx: use VENDORSPEC_FRC_SDCLK_ON when necessary

[Tom Rini]

On Tue, Feb 22, 2022 at 11:28:18AM +0800, haibo.chen at nxp.com wrote:

> From: Haibo Chen <haibo.chen at nxp.com>
> 
> After commit f132aab40327 ("Revert "mmc: fsl_esdhc_imx: use
> VENDORSPEC_FRC_SDCLK_ON to control card clock output""), it
> involve issue in mmc_switch_voltage(), because of the special
> design of usdhc.
> 
> For FSL_USDHC, it do not implement VENDORSPEC_CKEN/PEREN/HCKEN/IPGEN,
> these are reserved bits(Though RM contain the definition of these bits,
> but actually internal IC logic do not implement, already confirm with
> IC team). Instead, use VENDORSPEC_FRC_SDCLK_ON to gate on/off the card
> clock output. Here is the definition of this bit in RM:
> 
> [8] FRC_SDCLK_ON
> Force CLK output active
> Do not set this bit to 1 unless it is necessary. Also, make sure that
> this bit is cleared when uSDHC’s clock is about to be changed (frequency
> change, clock source change, or delay chain tuning).
> 0b - CLK active or inactive is fully controlled by the hardware.
> 1b - Force CLK active
> 
> In default, the FRC_SDCLK_ON is 0. This means, when there is no command
> or data transfer on bus, hardware will gate off the card clock. But in
> some case, we need the card clock keep on. Take IO voltage 1.8v switch
> as example, after IO voltage change to 1.8v, spec require gate off the
> card clock for 5ms, and gate on the clock back, once detect the card
> clock on, then the card will draw the dat0 to high immediately. If there
> is not clock gate off/on behavior, some card will keep the dat0 to low
> level. This is the reason we fail in mmc_switch_voltage().
> 
> To fix this issue, and concern that this is only the fsl usdhc hardware
> design limitation, set the bit FRC_SDCLK_ON in the beginning of the
> wait_dat0() and clear it in the end. To make sure the 1.8v IO voltage
> switch process align with SD specification.
> 
> For standard tuning process, usdhc specification also require the card
> clock keep on, so also add these behavior in fsl_esdhc_execute_tuning().
> 
> Reviewed-by: Marek Vasut <marex at denx.de>
> Tested-by: Fabio Estevam <festevam at gmail.com>
> Signed-off-by: Haibo Chen <haibo.chen at nxp.com>
> Reviewed-by: Peng Fan <peng.fan at nxp.com>
> Reviewed-by: Jaehoon Chung <jh80.chung at samsung.com>
> ---
>  drivers/mmc/fsl_esdhc_imx.c | 25 ++++++++++++++++++++++---
>  include/fsl_esdhc_imx.h     |  2 ++
>  2 files changed, 24 insertions(+), 3 deletions(-)

Is this going to get picked up in the imx or mmc trees soon, or should I
take this directly?  Thanks!

-- 
Tom
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