Re: [PATCH 1/1] scsi: ufs: make UFS Tx lane1 clock optional

[cang]

Hi Doug,

Really thank you for your review.

On 2018-10-10 05:56, Doug Anderson wrote:
> Hi,
>
> On Sun, Oct 7, 2018 at 9:34 PM Can Guo <cang@xxxxxxxxxxxxxx> wrote:
> > From: Venkat Gopalakrishnan <venkatg@xxxxxxxxxxxxxx>
> >
> > The UFS Tx lane1 clock could be muxed, hence keep it optional by 
> > ignoring
> > it if it is not provided in device tree.
>
> Thanks for the updated commit message.  This makes much more sense now! 
>  :-)

Yeah, sorry for making you guys confused. My bad previously.

> > @@ -113,10 +110,10 @@ static void ufs_qcom_disable_lane_clks(struct 
> > ufs_qcom_host *host)
> >         if (!host->is_lane_clks_enabled)
> >                 return;
> >
> > -       if (host->hba->lanes_per_direction > 1)
> > +       if (host->tx_l1_sync_clk)
> >                 clk_disable_unprepare(host->tx_l1_sync_clk);
>
> I don't believe you need the "if".  A NULL clock is by definition OK
> to enable / disable which is designed to make optional clocks easier
> to deal with.

You are right, I checked the implemention, clock enable/disable func 
would
bail out if clk is NULL just as your comments.

> >         clk_disable_unprepare(host->tx_l0_sync_clk);
> > -       if (host->hba->lanes_per_direction > 1)
> > +       if (host->rx_l1_sync_clk)
> >                 clk_disable_unprepare(host->rx_l1_sync_clk);
>
> optional: Technically this part of the patch wasn't actually needed,
> right?  "rx_l1_sync_clk" is not optional so that means that
> "rx_l1_sync_clk" should be non-NULL exactly when lanes_per_direction >
> 1.
>
> ...but actually I'm fine with keeping this part of your patch for
> symmetry.  Especially since you can leverage the
> clk_disable_unprepare(NULL) to simplify your code.  Please mention in
> your commit message that this is a cleanup and just for symmetry.
> Probably also remove the "if" tests that are guarding
> ufs_qcom_host_clk_enable().

Sure, got it.

> >         clk_disable_unprepare(host->rx_l0_sync_clk);
> >
> > @@ -141,24 +138,21 @@ static int ufs_qcom_enable_lane_clks(struct 
> > ufs_qcom_host *host)
> >         if (err)
> >                 goto disable_rx_l0;
> >
> > -       if (host->hba->lanes_per_direction > 1) {
> > +       if (host->rx_l1_sync_clk) {
>
> Similar: the above change isn't required but I'm OK if you want to
> make this change for symmetry / to cleanup clock handling.  Please
> mention in your commit message.

Sure, shall do so.

> > +       /* The tx lane1 clk could be muxed, hence keep this optional 
> > */
> > +       if (host->tx_l1_sync_clk)
> > +               ufs_qcom_host_clk_enable(dev, "tx_lane1_sync_clk",
> > +                                        host->tx_l1_sync_clk);
>
> If "host->tx_l1_sync_clk" is provided then you should still check the
> return value of ufs_qcom_host_clk_enable(), right?  ...so please leave
> the error path here.

Yeah... you are right.

> > @@ -174,23 +168,33 @@ static int ufs_qcom_init_lane_clks(struct 
> > ufs_qcom_host *host)
> >
> >         err = ufs_qcom_host_clk_get(dev,
> >                         "rx_lane0_sync_clk", &host->rx_l0_sync_clk);
> > -       if (err)
> > +       if (err) {
> > +               dev_err(dev, "%s: failed to get rx_lane0_sync_clk, err 
> > %d",
> > +                               __func__, err);
>
> nit: including "__func__" in dev_xxx() calls is discouraged.  The
> "dev_xxx" calls already print the device name and the string within a
> given device driver should be unique enough so __func__ just adds crap
> to the logs.  If you really feel that __func__ adds something for you,
> try posting up a patch to make all "dev_err" functions include
> __func__.  ...but I think you'd probably be rejected.
>
> suggestion: you'd save a few lines of code and simplify your probe if
> you just passed an "optional" bool to the ufs_qcom_host_clk_get() that
> controlled the printout.

Good idea!

> > -               err = ufs_qcom_host_clk_get(dev, "tx_lane1_sync_clk",
> > -                       &host->tx_l1_sync_clk);
> > +               /* The tx lane1 clk could be muxed, hence keep this 
> > optional */
> > +               ufs_qcom_host_clk_get(dev, "tx_lane1_sync_clk",
> > +                                       &host->tx_l1_sync_clk);
>
> To be technically correct you should actually check the error value
> returned by ufs_qcom_host_clk_get().  Specifically figure out what the
> error value is when "tx_lane1_sync_clk" isn't specified and check for
> that.
>
> ...one reason this matters is -EPROBE_DEFER.  In theory devm_clk_get()
> could return -EPROBE_DEFER.  In such a case you'd want to exit the
> probe, not continue on.  It's also just good coding practice to handle
> just the error you want though so that if the function returned some
> other failing case you'd propagate it down instead of eating it.
>
> If you passed "optional" to ufs_qcom_host_clk_get() as suggested above
> you could put this error-code checking in ufs_qcom_host_clk_get() and
> return 0 from that function if an optional clock was found to not
> exist.
>
> -Doug

I think I understand it. Thanks a lot for the thorough review and 
suggestions.

-Can Guo