Re: [PATCH] clocksource/drivers/tango-xtal: Replace code by clocksource_mmio_init

Thomas Gleixner
2015-11-13T15:27:30Z

On Fri, 13 Nov 2015, Marc Gonzalez wrote:
> On 13/11/2015 15:16, Daniel Lezcano wrote:
> > For example:
> >
> > struct clockcommon {
> > u32 mult;
> > u32 shift;
> > int rating;
> > void __iomem *base;
> > char *name;
> > int irq;
> > };
> >
> > struct clocksource {
> > struct clockcommon common; /* MUST be the first field */
> > cycle_t (*read)(struct clocksource *cs);
> > cycle_t mask;
> > ...
> > };
>
> According to my notes, commit 369db4c952 grouped hot-path data
> into a single cache line (hence ____cacheline_aligned).
>
> (AFAIR, ARMv7 ARCH_MULTIPLATFORM assumes CACHE_LINE=64)
>
> Not sure how to make the two concepts (common base struct and
> grouping hot data) play nicely, without wasting a lot of space
> on padding.

It wont play well. We are not going to change the layout of struct
clocksource because it will hurt the sane use cases for no reason.

Thanks,

tglx