linux-kernel - Re: [PATCH v2 12/12] ipu3-cio2: Add cio2-bridge to ipu3-cio2 driver

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Message-ID: <5515a4df-d224-1279-ab8d-40b848a74c38@gmail.com>
Date:   Sat, 19 Dec 2020 23:24:48 +0000
From:   Daniel Scally <djrscally@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-media@...r.kernel.org, devel@...ica.org, rjw@...ysocki.net,
        lenb@...nel.org, gregkh@...uxfoundation.org, yong.zhi@...el.com,
        sakari.ailus@...ux.intel.com, bingbu.cao@...el.com,
        tian.shu.qiu@...el.com, mchehab@...nel.org, robert.moore@...el.com,
        erik.kaneda@...el.com, pmladek@...e.com, rostedt@...dmis.org,
        sergey.senozhatsky@...il.com, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk,
        laurent.pinchart+renesas@...asonboard.com,
        jacopo+renesas@...ndi.org, kieran.bingham+renesas@...asonboard.com,
        linus.walleij@...aro.org, heikki.krogerus@...ux.intel.com,
        kitakar@...il.com, jorhand@...ux.microsoft.com
Subject: Re: [PATCH v2 12/12] ipu3-cio2: Add cio2-bridge to ipu3-cio2 driver

On 19/12/2020 00:39, Laurent Pinchart wrote:
> Hi Daniel,
> 
> On Fri, Dec 18, 2020 at 11:57:54PM +0000, Daniel Scally wrote:
>> Hi Laurent - thanks for the comments
>>
>> On 18/12/2020 16:53, Laurent Pinchart wrote:
>>>> +static void cio2_bridge_init_property_names(struct cio2_sensor *sensor)
>>>> +{
>>>> +	strscpy(sensor->prop_names.clock_frequency, "clock-frequency",
>>>> +		sizeof(sensor->prop_names.clock_frequency));
>>>> +	strscpy(sensor->prop_names.rotation, "rotation",
>>>> +		sizeof(sensor->prop_names.rotation));
>>>> +	strscpy(sensor->prop_names.bus_type, "bus-type",
>>>> +		sizeof(sensor->prop_names.bus_type));
>>>> +	strscpy(sensor->prop_names.data_lanes, "data-lanes",
>>>> +		sizeof(sensor->prop_names.data_lanes));
>>>> +	strscpy(sensor->prop_names.remote_endpoint, "remote-endpoint",
>>>> +		sizeof(sensor->prop_names.remote_endpoint));
>>>> +	strscpy(sensor->prop_names.link_frequencies, "link-frequencies",
>>>> +		sizeof(sensor->prop_names.link_frequencies));
>>>
>>> Just curious, was there anything not working correctly with the proposal
>>> I made ?
>>>
>>> static const struct cio2_property_names prop_names = {
>>> 	.clock_frequency = "clock-frequency",
>>> 	.rotation = "rotation",
>>> 	.bus_type = "bus-type",
>>> 	.data_lanes = "data-lanes",
>>> 	.remote_endpoint = "remote-endpoint",
>>> };
>>>
>>> static void cio2_bridge_init_property_names(struct cio2_sensor *sensor)
>>> {
>>> 	sensor->prop_names = prop_names;
>>> }
>>>
>>> It generates a warning when the string is too long for the field size,
>>> which should help catching issues at compilation time.
>>
>> Yes, though I don't know how much of a real-world problem it would have
>> been - if you recall we have the issue that the device grabs a reference
>> to the software_nodes (after we stopped delaying until after the
>> i2c_client is available), which means we can't safely free the
>> cio2_bridge struct on module unload. That also means we can't rely on
>> those pointers to string literals existing, because if the ipu3-cio2
>> module gets unloaded they'll be gone.
> 
> But the strings above are not stored as literals in .rodata, they're
> copied in prop_names (itself in .rodata), which is then copied to
> sensor->prop_names.

Yeah, my bad; I also had changed the struct definition to:

struct cio2_property_names {
	char *clock_frequency;
	...
};

And that behaves differently - apologies. I'll change to your proposal.