Re: [PATCH v6 3/4] clocksource/drivers: Add a goldfish-timer clocksource

[Laurent Vivier]

Le 14/01/2022 à 12:12, Geert Uytterhoeven a écrit :
> Hi Laurent,
>
> On Fri, Jan 14, 2022 at 12:03 PM Laurent Vivier <laurent@xxxxxxxxx> wrote:
> > Le 14/01/2022 à 11:46, Arnd Bergmann a écrit :
> > > On Thu, Jan 13, 2022 at 9:19 PM Laurent Vivier <laurent@xxxxxxxxx> wrote:
> > > > +static int goldfish_timer_set_oneshot(struct clock_event_device *evt)
> > > > +{
> > > > +       struct goldfish_timer *timerdrv = ced_to_gf(evt);
> > > > +       void __iomem *base = timerdrv->base;
> > > > +
> > > > +       __raw_writel(0, base + TIMER_ALARM_HIGH);
> > > > +       __raw_writel(0, base + TIMER_ALARM_LOW);
> > > > +       __raw_writel(1, base + TIMER_IRQ_ENABLED);
> > >
> > > As mentioned elsewhere, the __raw_* accessors are not portable, please
> > > use readl()/writel() here, or possibly ioread32_be()/iowrite32_be() for
> > > the big-endian variant.
> >
> > We can't use readl()/writel() here because it's supposed to read from a little endian device, and
> > goldfish endianness depends on the endianness of the machine.
> >
> > For goldfish, readl()/writel() works fine on little-endian machine but not on big-endian machine.
> >
> > On m68k, you have:
> >
> > #define readl(addr)      in_le32(addr)
> > #define writel(val,addr) out_le32((addr),(val))
> >
> > and with goldfish it's wrong as the device is not little-endian, it is big-endian like the machine.
> >
> > same comment with ioread32_be()/iowrite32_be(): it will work on big-endian machine not on little-endian.
> >
> > We need an accessor that doesn't byteswap the value, that accesses it natively, and in all other
> > parts of the kernel __raw_writel() and __raw_readl() are used.
>
> Hence Arnd's suggestion to define custom accessors in the Goldfish
> RTC driver, that map to {read,write}l() on little-endian, and to
> io{read,write}32_be() on big-endian.
>
> BTW, I'd go for io{read,write}32() on little endian instead, for
> symmetry.

You mean something like that:

#ifdef CONFIG_CPU_BIG_ENDIAN
#define raw_ioread32 ioread32be
#define raw_iowrite32 iowrite32be
#else
#define raw_ioread32 ioread32
#define raw_iowrite32 iowrite32
#endif

and then use raw_ioread32()/raw_iowrite32() rather than readl()/writel()?

Thanks,
Laurent