Re: [PATCHv14 2/9] coresight: etm4x: Use asm-generic IO memory barriers

[Sai Prakash Ranjan <quic_saipraka@quicinc.com>]

Hi Suzuki,

On 5/6/2022 5:14 AM, Suzuki K Poulose wrote:
> Hi,
>
> On 04/05/2022 12:28, Sai Prakash Ranjan wrote:
>> Per discussion in [1], it was decided to move to using architecture
>> independent/asm-generic IO memory barriers to have just one set of
>> them and deprecate use of arm64 specific IO memory barriers in driver
>> code. So replace current usage of __io_rmb()/__iowmb() in drivers to
>> __io_ar()/__io_bw().
>>
>> [1] https://lore.kernel.org/lkml/CAK8P3a0L2tLeF1Q0+0ijUxhGNaw+Z0fyPC1oW6_ELQfn0=i4iw@mail.gmail.com/
>>
>
> Looking at the dis-assembly it looks like in effect they are slightly
> different for arm64.
>
> i.e., before this patch we had
>
> "dmb osh{ld/st}"
>
> and after the patch we have :
>
> "dsb {ld/st}"
>
> Is this really what we want ? I don't think this is desirable.
>
> Suzuki
>

No, this is not supposed to happen and I do not see how it could happen.
__io_ar() is defined as __iormb() and __io_bw() is __iowmb().

I checked the disassembly in both case with MMIO trace off/on with __etm4_cpu_save()
as below and saw the same number of "dmb"s.

aarch64-linux-gnu-gdb -batch -ex "disassemble/rs __etm4_cpu_save" vmlinux-without-mmio
aarch64-linux-gnu-gdb -batch -ex "disassemble/rs __etm4_cpu_save" vmlinux-with-mmio

Can you tell me how are you validating if I am missing something?

Thanks,
Sai

>
>> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
>> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
>> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@quicinc.com>
>> Reviewed-by: Arnd Bergmann <arnd@arndb.de>
>> ---
>>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 8 ++++----
>>   drivers/hwtracing/coresight/coresight-etm4x.h      | 8 ++++----
>>   2 files changed, 8 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> index 7f416a12000e..81c0faf45b28 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> @@ -98,7 +98,7 @@ u64 etm4x_sysreg_read(u32 offset, bool _relaxed, bool _64bit)
>>       }
>>         if (!_relaxed)
>> -        __iormb(res);    /* Imitate the !relaxed I/O helpers */
>> +        __io_ar(res);    /* Imitate the !relaxed I/O helpers */
>>         return res;
>>   }
>> @@ -106,7 +106,7 @@ u64 etm4x_sysreg_read(u32 offset, bool _relaxed, bool _64bit)
>>   void etm4x_sysreg_write(u64 val, u32 offset, bool _relaxed, bool _64bit)
>>   {
>>       if (!_relaxed)
>> -        __iowmb();    /* Imitate the !relaxed I/O helpers */
>> +        __io_bw();    /* Imitate the !relaxed I/O helpers */
>>       if (!_64bit)
>>           val &= GENMASK(31, 0);
>>   @@ -130,7 +130,7 @@ static u64 ete_sysreg_read(u32 offset, bool _relaxed, bool _64bit)
>>       }
>>         if (!_relaxed)
>> -        __iormb(res);    /* Imitate the !relaxed I/O helpers */
>> +        __io_ar(res);    /* Imitate the !relaxed I/O helpers */
>>         return res;
>>   }
>> @@ -138,7 +138,7 @@ static u64 ete_sysreg_read(u32 offset, bool _relaxed, bool _64bit)
>>   static void ete_sysreg_write(u64 val, u32 offset, bool _relaxed, bool _64bit)
>>   {
>>       if (!_relaxed)
>> -        __iowmb();    /* Imitate the !relaxed I/O helpers */
>> +        __io_bw();    /* Imitate the !relaxed I/O helpers */
>>       if (!_64bit)
>>           val &= GENMASK(31, 0);
>>   diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
>> index 3c4d69b096ca..f54698731582 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm4x.h
>> +++ b/drivers/hwtracing/coresight/coresight-etm4x.h
>> @@ -448,14 +448,14 @@
>>   #define etm4x_read32(csa, offset)                    \
>>       ({                                \
>>           u32 __val = etm4x_relaxed_read32((csa), (offset)); \
>> -        __iormb(__val);                        \
>> +        __io_ar(__val);                        \
>>           __val;                            \
>>        })
>>     #define etm4x_read64(csa, offset)                    \
>>       ({                                \
>>           u64 __val = etm4x_relaxed_read64((csa), (offset)); \
>> -        __iormb(__val);                        \
>> +        __io_ar(__val);                        \
>>           __val;                            \
>>        })
>>   @@ -479,13 +479,13 @@
>>     #define etm4x_write32(csa, val, offset)                    \
>>       do {                                \
>> -        __iowmb();                        \
>> +        __io_bw();                        \
>>           etm4x_relaxed_write32((csa), (val), (offset)); \
>>       } while (0)
>>     #define etm4x_write64(csa, val, offset)                    \
>>       do {                                \
>> -        __iowmb();                        \
>> +        __io_bw();                        \
>>           etm4x_relaxed_write64((csa), (val), (offset)); \
>>       } while (0)
>