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

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

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?


>
>>
>> > 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
>> >