Message-ID: <4212ba2d-0fe0-4b6c-9acb-1359e7b9ffa0@linux.dev>
Date: Sun, 28 Apr 2024 04:10:55 +0800
From: Sui Jingfeng <sui.jingfeng@...ux.dev>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss
 <rfoss@...nel.org>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Andrzej Hajda <andrzej.hajda@...el.com>, Jonas Karlman <jonas@...boo.se>,
 Jernej Skrabec <jernej.skrabec@...il.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
 Phong LE <ple@...libre.com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 8/9] drm/bridge: tfp410: Use fwnode API to acquire
 device properties

Hi,


On 2024/4/28 03:17, Dmitry Baryshkov wrote:
> On Sun, Apr 28, 2024 at 02:43:20AM +0800, Sui Jingfeng wrote:
>> Hi,
>>
>>
>> On 2024/4/23 04:08, Dmitry Baryshkov wrote:
>>> On Tue, Apr 23, 2024 at 03:19:02AM +0800, Sui Jingfeng wrote:
>>>> Make this driver DT-independent by calling the freshly created helpers,
>>>> which reduce boilerplate and open the door for otherwise use cases. No
>>>> functional changes for DT based systems.
>>>>
>>>> Signed-off-by: Sui Jingfeng <sui.jingfeng@...ux.dev>
>>>> ---
>>>>    drivers/gpu/drm/bridge/ti-tfp410.c | 41 +++++++++++++++---------------
>>>>    1 file changed, 21 insertions(+), 20 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/bridge/ti-tfp410.c b/drivers/gpu/drm/bridge/ti-tfp410.c
>>>> index c7bef5c23927..58dc7492844f 100644
>>>> --- a/drivers/gpu/drm/bridge/ti-tfp410.c
>>>> +++ b/drivers/gpu/drm/bridge/ti-tfp410.c
>>>> @@ -266,8 +266,9 @@ static const struct drm_bridge_timings tfp410_default_timings = {
>>>>    static int tfp410_parse_timings(struct tfp410 *dvi, bool i2c)
>>>>    {
>>>> +	struct fwnode_handle *fwnode = dev_fwnode(dvi->dev);
>>>>    	struct drm_bridge_timings *timings = &dvi->timings;
>>>> -	struct device_node *ep;
>>>> +	struct fwnode_handle *ep;
>>>>    	u32 pclk_sample = 0;
>>>>    	u32 bus_width = 24;
>>>>    	u32 deskew = 0;
>>>> @@ -288,14 +289,14 @@ static int tfp410_parse_timings(struct tfp410 *dvi, bool i2c)
>>>>    	 * and EDGE pins. They are specified in DT through endpoint properties
>>>>    	 * and vendor-specific properties.
>>>>    	 */
>>>> -	ep = of_graph_get_endpoint_by_regs(dvi->dev->of_node, 0, 0);
>>>> +	ep = fwnode_graph_get_endpoint_by_id(fwnode, 0, 0, 0);
>>>>    	if (!ep)
>>>>    		return -EINVAL;
>>>>    	/* Get the sampling edge from the endpoint. */
>>>> -	of_property_read_u32(ep, "pclk-sample", &pclk_sample);
>>>> -	of_property_read_u32(ep, "bus-width", &bus_width);
>>>> -	of_node_put(ep);
>>>> +	fwnode_property_read_u32(ep, "pclk-sample", &pclk_sample);
>>>> +	fwnode_property_read_u32(ep, "bus-width", &bus_width);
>>>> +	fwnode_handle_put(ep);
>>>>    	timings->input_bus_flags = DRM_BUS_FLAG_DE_HIGH;
>>>> @@ -324,7 +325,7 @@ static int tfp410_parse_timings(struct tfp410 *dvi, bool i2c)
>>>>    	}
>>>>    	/* Get the setup and hold time from vendor-specific properties. */
>>>> -	of_property_read_u32(dvi->dev->of_node, "ti,deskew", &deskew);
>>>> +	fwnode_property_read_u32(fwnode, "ti,deskew", &deskew);
>>>>    	if (deskew > 7)
>>>>    		return -EINVAL;
>>>> @@ -336,12 +337,12 @@ static int tfp410_parse_timings(struct tfp410 *dvi, bool i2c)
>>>>    static int tfp410_init(struct device *dev, bool i2c)
>>>>    {
>>>> -	struct device_node *node;
>>>> +	struct fwnode_handle *fwnode = dev_fwnode(dev);
>>>>    	struct tfp410 *dvi;
>>>>    	int ret;
>>>> -	if (!dev->of_node) {
>>>> -		dev_err(dev, "device-tree data is missing\n");
>>>> +	if (!fwnode) {
>>>> +		dev_err(dev, "firmware data is missing\n");
>>>>    		return -ENXIO;
>>>>    	}
>>>> @@ -352,8 +353,8 @@ static int tfp410_init(struct device *dev, bool i2c)
>>>>    	dvi->dev = dev;
>>>>    	dev_set_drvdata(dev, dvi);
>>>> +	drm_bridge_set_node(&dvi->bridge, fwnode);
>>>>    	dvi->bridge.funcs = &tfp410_bridge_funcs;
>>>> -	dvi->bridge.of_node = dev->of_node;
>>>>    	dvi->bridge.timings = &dvi->timings;
>>>>    	dvi->bridge.type = DRM_MODE_CONNECTOR_DVID;
>>>> @@ -362,15 +363,15 @@ static int tfp410_init(struct device *dev, bool i2c)
>>>>    		return ret;
>>>>    	/* Get the next bridge, connected to port@1. */
>>>> -	node = of_graph_get_remote_node(dev->of_node, 1, -1);
>>>> -	if (!node)
>>>> -		return -ENODEV;
>>>> -
>>>> -	dvi->next_bridge = of_drm_find_bridge(node);
>>>> -	of_node_put(node);
>>>> -
>>>> -	if (!dvi->next_bridge)
>>>> +	dvi->next_bridge = drm_bridge_find_next_bridge_by_fwnode(fwnode, 1);
>>>> +	if (IS_ERR(dvi->next_bridge)) {
>>>> +		ret = PTR_ERR(dvi->next_bridge);
>>>> +		dev_err(dev, "Error in founding the next bridge: %d\n", ret);
>>>> +		return ret;
>>> Same comment regarding dev_err_probe().
>>>
>>> LGTM otherwise.
>>
>> My drm_bridge_find_next_bridge_by_fwnode() function won't return -EPROBE_DEFER,
>> this is known for sure. this can be used as a prior(priori) knowledge. This is
>> intentionally by design.
>>
>>
>> Calling the dev_err_probe() just introduce extra overhead on non EPROBE_DEFER
>> cases. Hence, It is useless to use dev_err_probe() at here.
>>
>>
>>>> +	} else if (!dvi->next_bridge) {
>>>> +		dev_dbg(dev, "Next bridge not found, deferring probe\n");
>>>>    		return -EPROBE_DEFER;
>>> Looking at the bolerplate code, I think it would be better to make
>>> drm_bridge_find_next_bridge_by_fwnode() reutrn -EPROBE_DEFER on its own.
>>>
>> The drm_bridge_find_next_bridge_by_fwnode() function itself can not
>> reliable detect if the driver(the remote bridge) already probed or not.
>>
>> Hence, as a core helper function, we can not guarantee that return
>> -EPROBE_DEFER is always correct.
>>
>> While, return NULL is always correct. The NULL can stand for two meanings.
>> One is that the next bridge is really don't exist, may happen when the
>> caller provided a wrong fwnode argument.
> Please take a look at drm_of_find_panel_or_bridge().


The function name seems to hint that a panel is not a bridge, while panel can be drm bridge.
display connector can also be a bridge, display connector can also be within a bridge.
There also has HPD fake bridge.

so maybe drm_of_find_panel_or_connector_or_hpd_bridge()?


My function intend to use one word "bridge" stand for all at this moment.


> Returning specific
> error code is always better than returning just NULL. As you have
> pointed yourself, there are (at least) two cases when your function
> returns NULL. Caller can not identify them unless the function returns
> proper error code.

No, you miss the point.

The point is that the caller *don't need* to identify them.
Just tears down (quit with -EPROBE_DEFER returned) is enough.
This is also what's other drivers do.

>
>> Another case is that the next bridge exists but not probed yet, and
>> drm_bridge_find_next_bridge_by_fwnode() can return NULL when it gets called
>> too early.
>>
>> Therefore, it is better to left to the users of this function to process
>> the NULL return value. As driver instances has some extra prior knowledge.
>> And can be controlled by drm bridge driver author.
> he driver has no prior knowledge if there is a remote fwnode/ofnode or
> if there is none.

No,

  
As I have told you several time, the DT/fwnode graph speak everything.
Display bridge driver can query firmware(DT/ACPI) to know if the next bridge
is present, is it really meant to be used and how many bridges in the chains.

If there has complete OF/fwnode graph and the graph say that there has next
bridge in the chain. Then the driver has to return -EPROBE_DEFER if he can't
find the next.

And the most important thing is that it is the bridge drivers responsibility
or authority to take whatever actions when drm_bridge_find_next_bridge_by_fwnode()
can return NULL. Core helpers is meant to be lightweight only, there no need
to introduce this overhead.
  
Ok. I think I have been patient long enough.
You questions and/or reviews have been given polite replies, that's it.

>>>> +	}
>>>>    	/* Get the powerdown GPIO. */
>>>>    	dvi->powerdown = devm_gpiod_get_optional(dev, "powerdown",
>>>> @@ -422,10 +423,10 @@ static struct platform_driver tfp410_platform_driver = {
>>>>    /* There is currently no i2c functionality. */
>>>>    static int tfp410_i2c_probe(struct i2c_client *client)
>>>>    {
>>>> +	struct fwnode_handle *fwnode = dev_fwnode(&client->dev);
>>>>    	int reg;
>>>> -	if (!client->dev.of_node ||
>>>> -	    of_property_read_u32(client->dev.of_node, "reg", &reg)) {
>>>> +	if (!fwnode || fwnode_property_read_u32(fwnode, "reg", &reg)) {
>>>>    		dev_err(&client->dev,
>>>>    			"Can't get i2c reg property from device-tree\n");
>>>>    		return -ENXIO;
>>>> -- 
>>>> 2.34.1
>>>>
>> -- 
>> Best regards,
>> Sui
>>
-- 
Best regards,
Sui

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