Hi Can,

On Wed, 2020-07-29 at 13:31 +0800, Can Guo wrote:

Hi Stanley,

On 2020-07-29 13:18, Stanley Chu wrote:

quoted

Some UFS devices require delay after VCC power rail is turned-off.
Introduce a device quirk "DELAY_AFTER_LPM" to add 5ms delays after
VCC power-off during suspend flow.

Just curious, I can understand if you want to add some delays before
turnning off VCC/VCCQ/VCCQ2, but what is the delay AFTER turnning
them off for? I mean the power has been cut by host from PMIC, how
can the delay benefit the UFS device?

The problem comes from both sides,
1. VCC power rail design by SoC vendors, and
2. Device strategy according to VCC changes

Take Micron UFS devices on MediaTek platform as example, our VCC drop
rate may be too slow and lead to incorrect resume strategy by device.
Without this delay, device may not resume successfully.

Thanks,
Stanley Chu


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