linux-kernel - Re: [PATCH v9 27/28] media: iris: enable video driver probe of SM8250 SoC

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Message-ID: <1bcf0995-cb77-4e01-b3e0-14f88dc91140@linaro.org>
Date: Wed, 15 Jan 2025 22:49:28 +0000
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Johan Hovold <johan@...nel.org>
Cc: Dikshita Agarwal <quic_dikshita@...cinc.com>,
 Vikash Garodia <quic_vgarodia@...cinc.com>,
 Abhinav Kumar <quic_abhinavk@...cinc.com>,
 Mauro Carvalho Chehab <mchehab@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>,
 Hans Verkuil <hverkuil@...all.nl>,
 Sebastian Fricke <sebastian.fricke@...labora.com>,
 Neil Armstrong <neil.armstrong@...aro.org>,
 Nicolas Dufresne <nicolas@...fresne.ca>,
 Uwe Kleine-König <u.kleine-koenig@...libre.com>,
 Jianhua Lu <lujianhua000@...il.com>,
 Stefan Schmidt <stefan.schmidt@...aro.org>, linux-media@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Bjorn Andersson <andersson@...nel.org>
Subject: Re: [PATCH v9 27/28] media: iris: enable video driver probe of SM8250
 SoC

On 10/01/2025 00:12, Dmitry Baryshkov wrote:
> On Thu, Jan 09, 2025 at 04:11:04PM +0100, Johan Hovold wrote:
>> On Thu, Dec 12, 2024 at 05:21:49PM +0530, Dikshita Agarwal wrote:
>>> Initialize the platform data and enable video driver probe of SM8250
>>> SoC. Add a kernel param to select between venus and iris drivers for
>>> platforms supported by both drivers, for ex: SM8250.
>>
>> Why do you want to use a module parameter for this? What would be the
>> default configuration? (Module parameters should generally be avoided.)
>>
>> Why not simply switch to the new driver (and make sure that the new
>> driver is selected if the old one was enabled in the kernel config)?
> 
> Because the new driver doesn't yet have feature parity with the venus
> driver. So it was agreed that developers provide upgrade path to allow
> users to gradually test and switch to the new driver. When the feature
> parity is achieved, the plan is to switch default to point to the Iris
> driver, then after a few releases start removing platforms from Venus.
> 
>>> Tested-by: Stefan Schmidt <stefan.schmidt@...aro.org> # x1e80100 (Dell
>>
>> Looks like something is missing from Stefan's Tested-by tag throughout
>> the series ("Dell XPS13"?)
>>
>>> Reviewed-by: Stefan Schmidt <stefan.schmidt@...aro.org>
>>> Signed-off-by: Dikshita Agarwal <quic_dikshita@...cinc.com>
>>   
>>> +static bool prefer_venus = true;
>>> +MODULE_PARM_DESC(prefer_venus, "Select whether venus or iris driver should be preferred");
>>> +module_param(prefer_venus, bool, 0444);
>>> +
>>> +/* list all platforms supported by only iris driver */
>>> +static const char *const iris_only_platforms[] = {
>>> +	"qcom,sm8550-iris",
>>> +	NULL,
>>> +};
>>
>> Surely you don't want to have to add every new platform to two tables
>> (i.e. the id table and again here).
> 
> I'd agree here, this list should go. We should only list platforms under
> the migration.
> 
>>
>>> +
>>> +/* list all platforms supported by both venus and iris drivers */
>>> +static const char *const venus_to_iris_migration[] = {
>>> +	"qcom,sm8250-venus",
>>> +	NULL,
>>> +};
>>> +
>>> +static bool video_drv_should_bind(struct device *dev, bool is_iris_driver)
> 
> The name should follow other names in the driver.
> `video_drv_should_bind` doesn't have a common prefix.
> 
> Also export it and use it from the venus driver if Iris is enabled.
> 
>>> +{
>>> +	if (of_device_compatible_match(dev->of_node, iris_only_platforms))
>>> +		return is_iris_driver;
>>> +
>>> +	/* If it is not in the migration list, use venus */
>>> +	if (!of_device_compatible_match(dev->of_node, venus_to_iris_migration))
>>> +		return !is_iris_driver;
>>> +
>>> +	return prefer_venus ? !is_iris_driver : is_iris_driver;
>>> +}
>>> +
>>>   static int iris_probe(struct platform_device *pdev)
>>>   {
>>>   	struct device *dev = &pdev->dev;
>>> @@ -196,6 +224,9 @@ static int iris_probe(struct platform_device *pdev)
>>>   	u64 dma_mask;
>>>   	int ret;
>>>   
>>> +	if (!video_drv_should_bind(&pdev->dev, true))
>>> +		return -ENODEV;
>>
>> AFAICT nothing is preventing venus from binding even when 'prefer_venus'
>> is false.
>>
>>> +
>>>   	core = devm_kzalloc(&pdev->dev, sizeof(*core), GFP_KERNEL);
>>>   	if (!core)
>>>   		return -ENOMEM;
>>> @@ -324,6 +355,10 @@ static const struct of_device_id iris_dt_match[] = {
>>>   		.compatible = "qcom,sm8550-iris",
>>>   		.data = &sm8550_data,
>>>   	},
>>> +	{
>>> +		.compatible = "qcom,sm8250-venus",
>>> +		.data = &sm8250_data,
>>> +	},
>>>   	{ },
>>>   };
>>>   MODULE_DEVICE_TABLE(of, iris_dt_match);
>>
>> Johan
> 

One drawback to this approach is; if CONFIG_QCOM_VENUS=n and 
CONFIG_QCOM_IRIS=m you still need to-do

zcat /proc/config.gz | grep -e VENUS -e IRIS
CONFIG_VIDEO_QCOM_IRIS=m
# CONFIG_VIDEO_QCOM_VENUS is not set

rmmod iris
modprobe iris prefer_venus=0

which is awkward.

Certainly if venus is off the parameter should default to false.

Perhaps I've missed the resolution of this discussion but how exactly 
are we fixing the "racy" nature of binding here ?

Shouldn't there be a parallel venus patch which either has its own 
module parameter to quiesce binding in favour of iris ?

i.e if

CONFIG_QCOM_VENUS=m and CONFIG_QCOM_IRIS=m

rmmod iris
rmmod venus

(sleep $((RANDOM % 3600)); (modprobe iris prefer_venus=0) &> /dev/null & 
disown) &

(sleep $((RANDOM % 3600)); (modprobe venus) &> /dev/null & disown) &

Will do what exactly ?

---
bod