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

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Date:   Fri, 6 May 2022 00:44:42 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Sai Prakash Ranjan <quic_saipraka@...cinc.com>, arnd@...db.de,
        catalin.marinas@....com, rostedt@...dmis.org
Cc:     gregkh@...uxfoundation.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        maz@...nel.org, quic_psodagud@...cinc.com, quic_tsoni@...cinc.com,
        will@...nel.org, Mathieu Poirier <mathieu.poirier@...aro.org>
Subject: Re: [PATCHv14 2/9] coresight: etm4x: Use asm-generic IO memory
 barriers

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


> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Suzuki K Poulose <suzuki.poulose@....com>
> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@...cinc.com>
> Reviewed-by: Arnd Bergmann <arnd@...db.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)
>