Re: [PATCH v3] clk: set initial best mux parent to current parent with CLK_MUX_ROUND_CLOSEST

[Yang Xiwen]

On 3/7/2024 4:48 PM, Maxime Ripard wrote:
> Hi,
>
> On Thu, Mar 07, 2024 at 10:03:50AM +0800, Yang Xiwen via B4 Relay wrote:
> > From: Yang Xiwen <forbidden405@xxxxxxxxxxx>
> >
> > Originally, the initial clock rate is hardcoded to 0, this can lead to
> > some problem when setting a very small rate with CLK_MUX_ROUND_CLOSEST.
> >
> > For example, if the lowest possible rate provided by the mux is 1000Hz,
> > setting a rate below 500Hz will fail, because no clock can provide a
> > better rate than the non-existant 0Hz. But it should succeed with 1000Hz
> > being set.
> >
> > Setting the initial best parent to current parent could solve this bug.
> >
> > Signed-off-by: Yang Xiwen <forbidden405@xxxxxxxxxxx>
> I don't think it would be the way to go. The biggest issue to me is that
> it's inconsistent, and only changing the behaviour for a given flag
> doesn't solve that.


I think the current behavior is odd but conforms to the document if 
CLK_MUX_ROUND_CLOSEST is not specified. If i understand correctly, the 
default behavior of mux clocks is to select the closest rate lower than 
requested rate, and CLK_MUX_ROUND_CLOSEST removes the "lower than" 
limitation, which is what this version tries to accomplish.


> And again, either way, we should document it. And run it through kernelci.
>
> Maxime


--
Regards,
Yang Xiwen