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

[Can Guo]

On 2021-01-05 15:33, Adrian Hunter wrote:
> On 5/01/21 9:28 am, Can Guo wrote:
> > On 2021-01-05 15:16, Adrian Hunter wrote:
> > > On 4/01/21 8:55 pm, Bjorn Andersson wrote:
> > > > On Mon 04 Jan 03:15 CST 2021, Adrian Hunter wrote:
> > > >
> > > > > On 22/12/20 3:49 pm, Ziqi Chen wrote:
> > > > > > 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?
> > >
> > > Yes
> > >
> > > >                         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?
> > >
> > > Functionally, doing a device reset is not the same as adjusting 
> > > signal
> > > levels to meet power up/off ramp requirements.  However, the issue is 
> > > that
> > > we do not use regulators, so the power is not necessarily being 
> > > changed at
> > > those points, and we definitely do not want to reset instead of 
> > > entering
> > > DeepSleep for example.
> > >
> > > Off the top of my head, I imagine something like a callback called
> > > ufshcd_vops_prepare_power_ramp(hba, bool on) which is called only if
> > > hba->vreg_info->vcc is not NULL.
> >
> > Hi Adrian,
> >
> > I don't see you have the vops device_reset() implemented anywhere in
> > current code base, how is this change impacting you? Do I miss 
> > anything
> > or are you planning to push a change which implements device_reset() 
> > soon?
>
> At some point, yes.

OK, then we don't even have to add a new vops, just go back to version 
#1 to
use ufshcd_vops_suspend() to control the device_reset. We took the hard 
way
because we wanted to fix it for all users.