Re: [PATCH RFC v4 1/1] scsi: ufs: Fix ufs power down/on specs violation

On Mon 04 Jan 03:15 CST 2021, Adrian Hunter wrote:

On 22/12/20 3:49 pm, Ziqi Chen wrote:

quoted

As per specs, e.g, JESD220E chapter 7.2, while powering
off/on the ufs device, RST_N signal and REF_CLK signal
should be between VSS(Ground) and VCCQ/VCCQ2.

To flexibly control device reset line, refactor the function
ufschd_vops_device_reset(sturct ufs_hba *hba) to ufshcd_
vops_device_reset(sturct ufs_hba *hba, bool asserted). The
new parameter "bool asserted" is used to separate device reset
line pulling down from pulling up.

This patch assumes the power is controlled by voltage regulators, but for us
it is controlled by firmware (ACPI), so it is not correct to change RST_n
for all host controllers as you are doing.

Also we might need to use a firmware interface for device reset, in which
case the 'asserted' value doe not make sense.

Are you saying that the entire flip-flop-the-reset is a single firmware
operation in your case? If you look at the Mediatek driver, the
implementation of ufs_mtk_device_reset_ctrl() is a jump to firmware.


But perhaps "asserted" isn't the appropriate English word for saying
"the reset is in the resetting state"?

I just wanted to avoid the use of "high"/"lo" as if you look at the
Mediatek code they pass the expected line-level to the firmware, while
in the Qualcomm code we pass the logical state to the GPIO code which is
setup up as "active low" and thereby flip the meaning before hitting the
pad.

Can we leave the device reset callback alone, and instead introduce a new
variant operation for setting RST_n to match voltage regulator power changes?

Wouldn't this new function just have to look like the proposed patches?
In which case for existing platforms we'd have both?

How would you implement this, or would you simply skip implementing
this?

Regards,
Bjorn


_______________________________________________
Linux-mediatek mailing list
Linux-mediatek@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-mediatek