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

[Potthuri, Sai Krishna]

Hi,

> -----Original Message-----
> From: Marek Vasut <marex at denx.de>
> Sent: Monday, October 17, 2022 7:41 PM
> To: Potthuri, Sai Krishna <sai.krishna.potthuri at amd.com>; Simek, Michal
> <michal.simek at amd.com>; linux-arm-kernel at lists.infradead.org
> Cc: Abhyuday Godhasara <abhyuday.godhasara at xilinx.com>; Harsha
> <harsha.harsha at xilinx.com>; Rajan Vaja <rajan.vaja at xilinx.com>; Ronak
> Jain <ronak.jain at xilinx.com>; Tanmay Shah <tanmay.shah at xilinx.com>
> Subject: Re: [PATCH] firmware: xilinx: Do not call IOCTL_SET_SD_TAPDELAY
> for value 0
> 
> On 10/17/22 16:04, Potthuri, Sai Krishna wrote:
> > Hi Marek Vasut,
> 
> Hi,
> 
> [...]
> 
> >> 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.
> > We got a similar issue from one of the customers saying tuning was
> > failing at lower temperatures with 4.19 kernel.
> > Root cause of this issue is incorrect tap delay sequence in 4.19
> > kernel which got fixed in 5.4 Xilinx Linux tree (2022.2 release).
> 
> I am not using the Xilinx downstream stuff, I am using linux-next and Linux
> 5.10.y from linux-stable for these tests.
> 
> > 4.19 sequence:
> > DLL assert->ITAP->DLL de-assert->DLL assert->OTAP->DLL de-assert
> > 5.4 sequence:
> > DLL assert->ITAP->OTAP->DLL de-assert
> >
> > Please give a try with the updated sequence.
> 
> Whatever fixes are in Linux 5.4 should already be present, and no, that does
> NOT work.
This fix has dependency on ATF version, are you testing with >=2.5 version?
https://github.com/ARM-software/arm-trusted-firmware/tree/v2.5

Regards
Sai Krishna
> 
> > Setting the tap delay value to Zero is required in some use cases
> > (Boot mode) to clear the previous software stack tap delay configurations.
> 
> The problem is that with SD0_ITAPDLYENA=1 and SD0_ITAPDLYSEL=0 the
> HS200 calibration fails, with SD0_ITAPDLYENA=0 and SD0_ITAPDLYSEL=0
> calibration succeeds.