On Tue, Aug 11, 2020 at 06:28:18PM +0200, Tomasz Figa wrote: > 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. That's a very good point. In case of ARM_ERRATA_754327, busy waiting should have a barrier thus cpu_relax() is desired. I guess the generic macro for busy waiting therefore should use them. Best regards, Krzysztof
