Re: [PATCH] ArmPkg/GenericWatchdogDxe: Split 64bit register write to 2x32bit

[Leif Lindholm <leif.lindholm@linaro.org>]

On Thu, Aug 02, 2018 at 08:32:18PM +0200, Ard Biesheuvel wrote:
> On 2 August 2018 at 17:12, Marcin Wojtas <mw@semihalf.com> wrote:
> > czw., 2 sie 2018 o 16:59 Ard Biesheuvel <ard.biesheuvel@linaro.org> napisał(a):
> >>
> >> On 2 August 2018 at 16:49, Marcin Wojtas <mw@semihalf.com> wrote:
> >> > EDK2 code uses a single 64bit write to update SBSA watchdog
> >> > compare registers, however an access to mmio registers should
> >> > be 32bit for some SoCs. Current usage of MmioWrite64 resulted
> >> > in an unpredicted behavior. Fix this by modifying
> >> > WatchdogWriteCompareRegister routine to use two consecutive
> >> > 32bit writes to Watchdog Compare Register Low and High.
> >> >
> >>
> >> You describe it as if this is generally the case, but this is just a
> >> silicon bug, right?
> >
> > Not sure if it's a bug, or simply SoC characterisctics to place SoC
> > registers to allow only mmio32 access to 32-bit registers. In any way,
> > even updated routine should be fine also for the ones capable of
> > mmio64 registers access. Do you have strong objections to the change?
> >
> 
> To be fair, the SBSA v5.0 does describe this register as
> 
> 0x010-0x013  WCV[31:0]   Watchdog compare value. Read/write registers
> 0x014-0x017  WCV[63:32]  containing the current value in the watchdog
>                          compare register.
> 
> so I guess it is implied that any implementation should tolerate this
> value being written as 2 32-bit quantities.
> 
> Leif?

Yep, the way the SBSA describes it, these are two separate 32-bit
registers, making accessing them with a single transaction ends up
being implementation defined behaviour.

We should maybe add separate _HIGH and _LOW #defines for the two rather
than calculating register addresses inline?

But apart from that:
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

> >
> >>
> >> > Contributed-under: TianoCore Contribution Agreement 1.1
> >> > Signed-off-by: Marcin Wojtas <mw@semihalf.com>
> >> > ---
> >> >  ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c | 6 +++++-
> >> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >> >
> >> > diff --git a/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c b/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c
> >> > index 3180f01..b25d210 100644
> >> > --- a/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c
> >> > +++ b/ArmPkg/Drivers/GenericWatchdogDxe/GenericWatchdogDxe.c
> >> > @@ -56,7 +56,11 @@ WatchdogWriteCompareRegister (
> >> >    UINT64  Value
> >> >    )
> >> >  {
> >> > -  MmioWrite64 (GENERIC_WDOG_COMPARE_VALUE_REG, Value);
> >> > +  MmioWrite32 (GENERIC_WDOG_COMPARE_VALUE_REG, Value & MAX_UINT32);
> >> > +  MmioWrite32 (
> >> > +    GENERIC_WDOG_COMPARE_VALUE_REG + sizeof (UINT32),
> >> > +    (Value >> 32) & MAX_UINT32
> >> > +    );
> >> >  }
> >> >
> >> >  VOID
> >> > --
> >> > 2.7.4
> >> >