linux-kernel - Re: [PATCH] coresight: etm4x: Enable ETE device accessed via MMIO

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Message-ID: <f7ccb9c4-60f4-7037-085d-3f36ae024219@arm.com>
Date:   Wed, 18 Oct 2023 09:28:59 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Ruidong Tian <tianruidong@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org
Cc:     james.clark@....com, coresight@...ts.linaro.org,
        mike.leach@...aro.org, alexander.shishkin@...ux.intel.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] coresight: etm4x: Enable ETE device accessed via MMIO

On 18/10/2023 08:05, Ruidong Tian wrote:
> The ETM4X driver now assume that all ETE as CPU system instructions
> accessed device, in fact the ETE device on some machines also accessed
> via MMIO.
> 
> Signed-off-by: Ruidong Tian <tianruidong@...ux.alibaba.com>

Why are we going backwards to MMIO from system instructions ? Is it 
because of an "unfriendly" hypervisor preventing access ?

As such, without a sufficiently acceptable explanation, I am reluctant
to make this change

Suzuki

> ---
>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 285539104bcc..ad298c9cc87e 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -1103,8 +1103,9 @@ static bool etm4_init_iomem_access(struct etmv4_drvdata *drvdata,
>   	 * with MMIO. But we cannot touch the OSLK until we are
>   	 * sure this is an ETM. So rely only on the TRCDEVARCH.
>   	 */
> -	if ((devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETMv4x_ARCH) {
> -		pr_warn_once("TRCDEVARCH doesn't match ETMv4 architecture\n");
> +	if ((devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETMv4x_ARCH &&
> +		(devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETE_ARCH) {
> +		pr_warn_once("TRCDEVARCH doesn't match ETMv4/ETE architecture\n");
>   		return false;
>   	}
>