linux-kernel - Re: [PATCH 1/2] firmware: qcom: scm: Return -EOPNOTSUPP for unsupported SHM bridge enabling

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Message-ID: <mgdj5xvqby3ftnnhma7dxvxskavx4p2pkzyorg4z3cza5xkimr@sqe4k2szwfbq>
Date: Sun, 6 Oct 2024 20:40:08 -0500
From: Bjorn Andersson <andersson@...nel.org>
To: Kuldeep Singh <quic_kuldsing@...cinc.com>
Cc: Konrad Dybcio <konradybcio@...nel.org>, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>, linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Qingqing Zhou <quic_qqzhou@...cinc.com>
Subject: Re: [PATCH 1/2] firmware: qcom: scm: Return -EOPNOTSUPP for
 unsupported SHM bridge enabling

On Sat, Oct 05, 2024 at 07:31:49PM GMT, Kuldeep Singh wrote:

Please shorten the subject a bit, perhaps:
"firmware: qcom: scm: Improve unsupported SHM bridge detection"

> From: Qingqing Zhou <quic_qqzhou@...cinc.com>
> 
> Currently for enabling shm bridge, QTEE will return 0 and put error 4 into

s/for/when/

> result[0] to qcom_scm for unsupported platform, tzmem will consider this
> as an unknown error not the unsupported case on the platform.
> 
> Error log:
> [    0.177224] qcom_scm firmware:scm: error (____ptrval____): Failed to enable the TrustZone memory allocator
> [    0.177244] qcom_scm firmware:scm: probe with driver qcom_scm failed with error 4
> 
> Change the function call qcom_scm_shm_bridge_enable() to remap this
> result[0] into the unsupported error and then tzmem can consider this as
> unsupported case instead of reporting an error.
> 

Sounds like we want a Fixes tag here.

> Signed-off-by: Qingqing Zhou <quic_qqzhou@...cinc.com>
> Co-developed-by: Kuldeep Singh <quic_kuldsing@...cinc.com>
> Signed-off-by: Kuldeep Singh <quic_kuldsing@...cinc.com>
> ---
>  drivers/firmware/qcom/qcom_scm.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
> index 10986cb11ec0..620313359042 100644
> --- a/drivers/firmware/qcom/qcom_scm.c
> +++ b/drivers/firmware/qcom/qcom_scm.c
> @@ -111,6 +111,10 @@ enum qcom_scm_qseecom_tz_cmd_info {
>  	QSEECOM_TZ_CMD_INFO_VERSION		= 3,
>  };
>  
> +enum qcom_scm_shm_bridge_result {
> +	SHMBRIDGE_RESULT_NOTSUPP	= 4,
> +};

This is not an enumeration, but a fixed defined constant. Please use
#define.

> +
>  #define QSEECOM_MAX_APP_NAME_SIZE		64
>  
>  /* Each bit configures cold/warm boot address for one of the 4 CPUs */
> @@ -1361,6 +1365,8 @@ EXPORT_SYMBOL_GPL(qcom_scm_lmh_dcvsh_available);
>  
>  int qcom_scm_shm_bridge_enable(void)
>  {
> +	int ret;
> +
>  	struct qcom_scm_desc desc = {
>  		.svc = QCOM_SCM_SVC_MP,
>  		.cmd = QCOM_SCM_MP_SHM_BRIDGE_ENABLE,
> @@ -1373,7 +1379,11 @@ int qcom_scm_shm_bridge_enable(void)
>  					  QCOM_SCM_MP_SHM_BRIDGE_ENABLE))
>  		return -EOPNOTSUPP;
>  
> -	return qcom_scm_call(__scm->dev, &desc, &res) ?: res.result[0];
> +	ret = qcom_scm_call(__scm->dev, &desc, &res);
> +	if (!ret && res.result[0] == SHMBRIDGE_RESULT_NOTSUPP)
> +		return -EOPNOTSUPP;
> +
> +	return ret ?: res.result[0];

I'd prefer, with the additional check, that you'd structure it like this:

	if (ret)
		return ret;

	if (res.result[0] == SHMBRIDGE_RESULT_NOTSUPP)
		return -EOPNOTSUPP;

	return res.result[0];


That way we deal with SCM-call errors first, otherwise we inspect and
act on the returned data.

That said, the return value of this function, if non-zero, will trickle
back to and be returned from qcom_scm_probe(), where Linux expects to
see a valid error code. Are there any other result[0] values we should
handle, which would allow us to end this function with "return 0"?

Regards,
Bjorn

>  }
>  EXPORT_SYMBOL_GPL(qcom_scm_shm_bridge_enable);
>  
> -- 
> 2.34.1
>