Re: [PATCH] clk: vc5: Abort clock configuration without upstream clock

[Stephen Boyd <sboyd@kernel.org>]

Quoting Laurent Pinchart (2018-12-29 08:34:18)
> Hi Stephen,
> 
> On Saturday, 29 December 2018 00:30:16 EET Stephen Boyd wrote:
> > Quoting Marek Vasut (2018-12-16 09:14:29)
> > > On 12/16/2018 08:19 AM, Laurent Pinchart wrote:
> > > > On Saturday, 15 December 2018 02:55:19 EET Marek Vasut wrote:
> > > >> In case the upstream clock are not set, which can happen in case the
> > > >> VC5 has no valid upstream clock, the $src variable is used uninited
> > > >> by regmap_update_bits(). Check for this condition and return -EINVAL
> > > >> in such case.
> > > > 
> > > > Note that the probe() function will fail in this case, so
> > > > vc5_mux_set_parent() won't be reached.
> > > > 
> > > >> Note that in case the VC5 has no valid upstream clock, the VC5 can
> > > >> not operate correctly. That is a hardware property of the VC5. The
> > > >> internal oscilator present in some VC5 models is also considered
> > > >> upstream clock.
> > > >> 
> > > >> Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
> > > >> Cc: Alexey Firago <alexey_firago@mentor.com>
> > > >> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > >> Cc: Stephen Boyd <sboyd@kernel.org>
> > > >> Cc: linux-renesas-soc@vger.kernel.org
> > > >> ---
> > > >> 
> > > >> NOTE: This is an updated version of:
> > > >>       https://patchwork.kernel.org/patch/10731699/
> > > >> 
> > > >> ---
> > > >> 
> > > >>  drivers/clk/clk-versaclock5.c | 4 +++-
> > > >>  1 file changed, 3 insertions(+), 1 deletion(-)
> > > >> 
> > > >> diff --git a/drivers/clk/clk-versaclock5.c
> > > >> b/drivers/clk/clk-versaclock5.c
> > > >> index 5b393e711e94..b10801506518 100644
> > > >> --- a/drivers/clk/clk-versaclock5.c
> > > >> +++ b/drivers/clk/clk-versaclock5.c
> > > >> @@ -262,8 +262,10 @@ static int vc5_mux_set_parent(struct clk_hw *hw,
> > > >> u8> index)
> > > >> 
> > > >>              if (vc5->clk_mux_ins == VC5_MUX_IN_XIN)
> > > >>                      src = VC5_PRIM_SRC_SHDN_EN_XTAL;
> > > >> -            if (vc5->clk_mux_ins == VC5_MUX_IN_CLKIN)
> > > >> +            else if (vc5->clk_mux_ins == VC5_MUX_IN_CLKIN)
> > > >>                      src = VC5_PRIM_SRC_SHDN_EN_CLKIN;
> > > >> +            else
> > > >> +                    return -EINVAL;
> > > >>      }
> > > > 
> > > > I'd rather go for Stephen's approach if the goal is just to silence a
> > > > warning for a condition that can't happen in practice.
> > > 
> > > Sure, probe will fail, but it's safer to handle the possibility that
> > > probe() is broken and this code is reached by properly handling the
> > > failure instead of doing something obviously wrong (like configuring the
> > > hardware with value 0).
> > 
> > I'm fine with this approach. Laurent?
> 
> So am I. I might add a comment in the vc5_mu_set_parent() function to explain 
> this can't happen.
> 

Ok. I can add a note and throw this into clk-fixes.