Re: [PATCH v3 04/12] scsi: ufs: core: Add support for TX Equalization

[Can Guo]

Hi Peter,

On 3/17/2026 9:08 PM, Peter Wang (王信友) wrote:
> On Tue, 2026-03-17 at 15:22 +0800, Can Guo wrote:
> > Here is the consideration:
> > 
> > 1. Scanning all 64 PreShoot/DeEmphasis combinations cost (much) more
> > time
> >    a. This could impact bootup KPI
> >    b. During TX EQTR, IOs are paused, when one conducts a re-
> > training,
> > the IOs could
> >         be paused for too long.
> > 
>
> Hi Can,
>
> Yes, it will take some time, but according to the specification,
> we need to find the best FOM, so the default value should still
> follow the specification.
It is just a default value of module parameter , one can change it via boot
cmdline. But since you have asked it twice, I will change the default 
value to
true in next version.
> > 2. As per our study in the past few months, the optimal/best
> > combination
> > is most
> >      likely within the 8 presets, which is true for both Host TX
> > lanes
> > and Device TX lanes.
> > 
>
> Host may be true, but there are so many devices, and new UFS 5.0
> devices will keep being released in the future. How can we
> guarantee that the optimal/best combination is most likely
> within the 8 presets?
>
>
> > 3. Even if sometime the optimal settings which fall out of the 8
> > presets, they are very
> >      close to optimal one found within the 8 presets.
> > 
>
> Could you share what led you to this conclusion?
>  From the scores reported by each vendor, it’s hard for us to
> determine what a difference of a few points actually means.
>
>
> > So, scanning the 8 presets only is more cost-efficient.
> > > 
> > > > +ufshcd_tx_eqtr_result_examine(struct ufshcd_tx_eq_params
> > > > *old_params,
> > > > +                             struct ufshcd_tx_eq_params
> > > > *new_params)
> > > > +{
> > > > +       int lane;
> > > > +
> > > > +       if (!old_params->is_valid)
> > > > +               return;
> > > 
> > > Is is_valid always false, causing a return here?
> > It can be valid if we are here (again) because one conducts a re-
> > training.
> > > 
>
> Then, should this function be moved to [07/12], which supports
> retraining?
Sure, I will move in next version.

Thanks,
Can Guo.
> Thanks.
> Peter
>
>
>
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