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

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Message-ID: <87f778cf-0e1e-4505-a0e8-7434316a9537@quicinc.com>
Date: Tue, 8 Oct 2024 02:10:02 +0530
From: Kuldeep Singh <quic_kuldsing@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>
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 10/7/2024 7:10 AM, Bjorn Andersson wrote:
> 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/

Ack.

> 
>> 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.

Ack.

> 
>> 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.

Ack.

>> +
>>  #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];

Sure, above looks more cleaner. Will update in next rev.

> 
> 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"?

As qcom_scm_shm_bridge_enable() is an shm enablement call, need to handle
supported(or unsupported) scenario appropriately and other errors can be
propagated to qcom_tzmem/qcom_scm_probe.

Please note, other return values(related to access control) from QTEE are
failures and do not require conversion to Linux error codes.

-- 
Regards
Kuldeep