Re: [PATCH v2 3/7] scsi: ufs: ufs-qcom: Allow the first init start with the maximum supported gear

[Can Guo]

Hi Mani,

On 11/8/2023 1:23 PM, Manivannan Sadhasivam wrote:
> On Mon, Nov 06, 2023 at 08:46:09PM -0800, Can Guo wrote:
> > From: Can Guo <quic_cang@xxxxxxxxxxx>
> >
> > During host driver init, the phy_gear is set to the minimum supported gear
> > (HS_G2). Then, during the first power mode change, the negotiated gear, say
> > HS-G4, is updated to the phy_gear variable so that in the second init the
> > updated phy_gear can be used to program the PHY.
> >
> > But the current code only allows update the phy_gear to a higher value. If
> > one wants to start the first init with the maximum support gear, say HS-G4,
> > the phy_gear is not updated to HS-G3 if the device only supports HS-G3.
>
> Can you elaborate when this can happen? AFAICS, there are 3 possibilities of
> initial phy gear with this series:
>
> 1. If ufshc is < 5.0, then G2 will be used.
> 2. If ufshc is >= 5.0 and if the version is populated in register, then that
> gear will be used. Most likely that gear can be G4/G5 depending on the device
> connected.
> 3. If ufshc is >=5.0 and version is not populated, then G4 will be used.
>
> In all the above cases, I do not see any necessity to switch the phy gear
> setting to lower one while scaling. Since the gears are backwards compatible,
> we always use one phy gear sequence. Moreover, we only have 2 init sequences.
>
> Please correct me if I'm missing anything.
>
> - Mani
In the next patch, I am setting the initial PHY gear to max HS gear read
from UFS host cap register, so that we don't need to keep updating the 
initial value for host->phy_gear for different HW versions in future. 
FYI, for HW ver 5 and 6, it is HS-G5. In future, the max gear might 
become HS-G6 or higher on newer HW verions.

I the case #3, if HS-G5 is set to host->phy_gear, the first init uses 
HS-G5, then after negotiation if the agreed gear is HS-G4, we need to 
update host->phy_gear to HS-G4 (a lower value) such that we use a power 
saving PHY gear settings during the 2nd init.

If the commit message is making you confused, I can update it in next 
version. Please let me if I made any mistakes here.

Thanks,
Can Guo.