Re: [PATCH] clk: mux: let clk_mux_val_to_index return U8_MAX in the error case

[Stephen Boyd <sboyd@kernel.org>]

Quoting Heiner Kallweit (2023-04-13 12:27:27)
> On 13.04.2023 21:10, Stephen Boyd wrote:
> > Quoting Heiner Kallweit (2023-04-11 23:19:04)
> >> Currently this function may return a negative errno, but almost no
> >> user checks for the error case. Only imx_clk_gpr_mux_get_parent()
> >> does, but mentions in a comment that they'd prefer a dummy value.
> >> Other users cast the negative errno to u8 instead, what may result
> >> in unwanted results.
> >> Let's deal with this by returning u8 and U8_MAX in the error case.
> >> Then clk_core_get_parent_by_index() can detect that the index is
> >> out of range.
> > 
> > Is this causing problems for you?
> 
> I'm not directly impacted. I came across this when working on a driver
> with the following scenario:
> 
> I have a clock muxer where I want to exclude one of the mux parents
> by using clk_mux.table. If by chance the boot loader used this mux
> parent, then clk_mux_val_to_index() would return an errno.
> Also within clk core the return value isn't checked in
> clk_mux_get_parent().
> 

Ok. I'd rather go with a total rewrite of the get_parent clk_op[1] and fix
this at the same time.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/clk/linux.git/log/?h=clk-parent-rewrite