[PATCH] firmware: xilinx: Do not call IOCTL_SET_SD_TAPDELAY for value 0

[Michal Simek]

+Sai

On 10/17/22 14:35, Marek Vasut wrote:
> In case the tap delay required by Arasan SDHCI is set to 0, the current
> embeddedsw firmware unconditionally writes IOU_SLCR SD_ITAPDLY to 0x100
> (SD0_ITAPDLYENA=1, SD0_ITAPDLYSEL=0). Previous behavior was to keep the
> IOU_SLCR SD_ITAPDLY set to 0x0. There is some sort of difference in the
> behavior between SD0_ITAPDLYENA=1/0 with the same SD0_ITAPDLYSEL=0, even
> though the behavior should be identical -- zero delay added to rxclk_in
> line. The former breaks HS200 training in low temperature conditions.
> 
> Avoid writing the IOU_SLCR SD_ITAPDLY register in case value is 0 to
> keep the register at value 0x0 to reinstate the previous behavior that
> was present in Xilinx downstream fork of Linux 4.19.y and which prevented
> breakage of HS200 training in low temperature conditions.
> 
> Note that the embeddedsw firmware does not permit clearing the SD_ITAPDLY
> SD0_ITAPDLYENA bit, this bit can only ever be set by the firmware and it
> is often impossible to update the possibly broken firmware.
> 
> Signed-off-by: Marek Vasut <marex at denx.de>
> ---
> Cc: Abhyuday Godhasara <abhyuday.godhasara at xilinx.com>
> Cc: Harsha <harsha.harsha at xilinx.com>
> Cc: Michal Simek <michal.simek at amd.com>
> Cc: Rajan Vaja <rajan.vaja at xilinx.com>
> Cc: Ronak Jain <ronak.jain at xilinx.com>
> Cc: Tanmay Shah <tanmay.shah at xilinx.com>
> To: linux-arm-kernel at lists.infradead.org
> ---
>   drivers/firmware/xilinx/zynqmp.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/firmware/xilinx/zynqmp.c b/drivers/firmware/xilinx/zynqmp.c
> index ff5cabe70a2b2..12712f64fb932 100644
> --- a/drivers/firmware/xilinx/zynqmp.c
> +++ b/drivers/firmware/xilinx/zynqmp.c
> @@ -738,6 +738,9 @@ EXPORT_SYMBOL_GPL(zynqmp_pm_get_pll_frac_data);
>    */
>   int zynqmp_pm_set_sd_tapdelay(u32 node_id, u32 type, u32 value)
>   {
> +	if (!value)
> +		return 0;
> +
>   	return zynqmp_pm_invoke_fn(PM_IOCTL, node_id, IOCTL_SET_SD_TAPDELAY,
>   				   type, value, NULL);
>   }