Messages in this thread | | | From | Tomasz Figa <> | Date | Tue, 11 Aug 2020 18:28:18 +0200 | Subject | Re: [PATCH v2] clk: samsung: Prevent potential endless loop in the PLL set_rate ops |
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2020年8月11日(火) 18:24 Krzysztof Kozlowski <krzk@kernel.org>: > > 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@samsung.com>: > > > > > > 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, Tomasz
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