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

From: Tomasz Figa
Date: Tue Aug 11 2020 - 12:28:32 EST

2020年8月11日(火) 18:24 Krzysztof Kozlowski <krzk@xxxxxxxxxx>:
> 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
> platforms,
> 2. it is a generic pattern for busy loops.
> On other architectures it could mean something (e.g. yield to other
> hyper-threading CPU).

Okay, thanks for confirming that it doesn't matter for us.

Now, I wonder if the readx_poll_*() helpers are supposed to take all
of those into account or on systems which would benefit from such
operations, it would be the caller's responsibility.

Best regards,