Re: [PATCH 4.4 017/192] [PATCH 017/135] clk: xgene: Fix divider with non-zero shift value

[Loc Ho]

Hi Ben,

>> >> ------------------
>> >>
>> >> [ Upstream commit 1382ea631ddddb634850a3795527db0feeff5aaf ]
>> >>
>> >> The X-Gene clock driver missed the divider shift operation when
>> >> set the divider value.
>> >>
>> >> Signed-off-by: Loc Ho <lho@xxxxxxx>
>> >> Fixes: 308964caeebc ("clk: Add APM X-Gene SoC clock driver")
>> >> Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
>> >> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
>> >> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>> >> ---
>> >>  drivers/clk/clk-xgene.c |    3 ++-
>> >>  1 file changed, 2 insertions(+), 1 deletion(-)
>> >>
>> >> --- a/drivers/clk/clk-xgene.c
>> >> +++ b/drivers/clk/clk-xgene.c
>> >> @@ -351,7 +351,8 @@ static int xgene_clk_set_rate(struct clk
>> >>               /* Set new divider */
>> >>               data = xgene_clk_read(pclk->param.divider_reg +
>> >>                               pclk->param.reg_divider_offset);
>> >> -             data &= ~((1 << pclk->param.reg_divider_width) - 1);
>> >> +             data &= ~((1 << pclk->param.reg_divider_width) - 1)
>> >> +                             << pclk->param.reg_divider_shift;
>> > [...]
>> >
>> > This still does the wrong thing when the shift value is non-zero: it
>> > clears all bits to the right of the divider field in data.  I think the
>> > correct assignment is:
>> >
>> >                 data &= ~(((1 << pclk->param.reg_divider_width) - 1)
>> >                           << pclk->param.reg_divider_shift);
>> >
>>
>> Yes... There was an later patch that address this -
>> https://patchwork.kernel.org/patch/8458361
>
> But it didn't go into this stable update, because you didn't point that
> out during review.

Sorry about this. I will keep this in mind in the future.

-Loc