Re: [PATCH 09/14] rpmsg: qcom_smd: Use qcom_smem_is_available()

From: Konrad Dybcio <konrad.dybcio@linaro.org>
To: Stephan Gerhold <stephan@gerhold.net>
Cc: Bjorn Andersson <andersson@kernel.org>,
	Andy Gross <agross@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Mathieu Poirier <mathieu.poirier@linaro.org>,
	linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-remoteproc@vger.kernel.org
Subject: Re: [PATCH 09/14] rpmsg: qcom_smd: Use qcom_smem_is_available()
Date: Mon, 5 Jun 2023 21:45:36 +0200	[thread overview]
Message-ID: <909e2780-80d1-3c9d-7be3-bd2d0c0c6e69@linaro.org> (raw)
In-Reply-To: <ZH407yP8RQmTlQtf@gerhold.net>


On 5.06.2023 21:18, Stephan Gerhold wrote:
> On Mon, Jun 05, 2023 at 08:56:44PM +0200, Konrad Dybcio wrote:
>>
>>
>> On 5.06.2023 09:08, Stephan Gerhold wrote:
>>> Rather than looking up a dummy item from SMEM, use the new
>>> qcom_smem_is_available() function to make the code more clear
>>> (and reduce the overhead slightly).
>>>
>>> Add the same check to qcom_smd_register_edge() as well to ensure that
>>> it only succeeds if SMEM is already available - if a driver calls the
>>> function and SMEM is not available yet then the initial state will be
>>> read incorrectly and the RPMSG devices might never become available.
>>>
>>> Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
>>> ---
>>>  drivers/rpmsg/qcom_smd.c | 10 +++++-----
>>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/rpmsg/qcom_smd.c b/drivers/rpmsg/qcom_smd.c
>>> index 7b9c298aa491..43f601c84b4f 100644
>>> --- a/drivers/rpmsg/qcom_smd.c
>>> +++ b/drivers/rpmsg/qcom_smd.c
>>> @@ -1479,6 +1479,9 @@ struct qcom_smd_edge *qcom_smd_register_edge(struct device *parent,
>>>  	struct qcom_smd_edge *edge;
>>>  	int ret;
>>>  
>>> +	if (!qcom_smem_is_available())
>>> +		return ERR_PTR(-EPROBE_DEFER);
>>> +
>>>  	edge = kzalloc(sizeof(*edge), GFP_KERNEL);
>>>  	if (!edge)
>>>  		return ERR_PTR(-ENOMEM);
>>> @@ -1553,12 +1556,9 @@ EXPORT_SYMBOL(qcom_smd_unregister_edge);
>>>  static int qcom_smd_probe(struct platform_device *pdev)
>>>  {
>>>  	struct device_node *node;
>>> -	void *p;
>>>  
>>> -	/* Wait for smem */
>>> -	p = qcom_smem_get(QCOM_SMEM_HOST_ANY, smem_items[0].alloc_tbl_id, NULL);
>>> -	if (PTR_ERR(p) == -EPROBE_DEFER)
>>> -		return PTR_ERR(p);
>>> +	if (!qcom_smem_is_available())
>>> +		return -EPROBE_DEFER;
>>>  
>>>  	for_each_available_child_of_node(pdev->dev.of_node, node)
>>>  		qcom_smd_register_edge(&pdev->dev, node);
>> Hm.. we're not checking the return value here, at all.. Perhaps that
>> could be improved and we could only check for smem presence inside
>> qcom_smd_register_edge()?
>>
> 
> I think the goal here it to register as many of the edges as possible,
> so we wouldn't necessarily want to abort if one of them fails. That's
> why it's enough to check for only for a possible -EPROBE_DEFER first.
Hm I guess that's the better option, killing the entire platform (no
rpm = no anything) because one edge failed to register would be not
very user friendly..

> 
> But more importantly after this series this is legacy code that exists
> only for backwards compatibility with older DTBs. The probe function
> won't be called for DTBs in mainline anymore. So I think it's not worth
> to improve it much anymore. ;)
Right!

Konrad
> 
> Thanks,
> Stephan