Re: [PATCH v2] clk: samsung: Prevent potential endless loop in the PLL set_rate ops

From: Krzysztof Kozlowski
Date: Tue Aug 11 2020 - 12:24:05 EST

On Tue, Aug 11, 2020 at 02:59:07PM +0200, Tomasz Figa wrote:
> Hi Sylwester,
> 2020年8月11日(火) 13:25 Sylwester Nawrocki <s.nawrocki@xxxxxxxxxxx>:
> >
> > In the .set_rate callback for some PLLs there is a loop polling state
> > of the PLL lock bit and it may become an endless loop when something
> > goes wrong with the PLL. For some PLLs there is already (a duplicated)
> > code for polling with timeout. This patch replaces that code with
> > the readl_relaxed_poll_timeout_atomic() macro and moves it to a common
> > helper function, which is then used for all the PLLs. The downside
> > of switching to the common macro is that we drop the cpu_relax() call.
> Tbh. I'm not sure what effect was exactly expected from cpu_relax() in
> the functions which already had timeout handling. Could someone shed
> some light on this?

For us, it should not matter much, except:
1. when on A9 with ARM_ERRATA_754327, but we do not enable it on our
2. it is a generic pattern for busy loops.

On other architectures it could mean something (e.g. yield to other
hyper-threading CPU).

Looks good.

Acked-by: Krzysztof Kozlowski <krzk@xxxxxxxxxx>

Best regards,