linux-kernel - Re: [PATCH v3] driver core: Explicitly initialize struct member @data.have_async in __device

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Message-ID: <692e27c4-a370-4920-819c-588f09892a3a@icloud.com>
Date: Sat, 14 Sep 2024 04:44:01 +0800
From: Zijun Hu <zijun_hu@...oud.com>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, linux-kernel@...r.kernel.org,
 Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH v3] driver core: Explicitly initialize struct member
 @data.have_async in __device_attach()

On 2024/9/14 01:39, Dmitry Torokhov wrote:
> Hi,
> 
> On Fri, Sep 13, 2024 at 10:05:38PM +0800, Zijun Hu wrote:
>> From: Zijun Hu <quic_zijuhu@...cinc.com>
>>
>> __device_attach() defines struct device_attach_data @data as auto
>> variable and needs to use both @data.want_async and @data.have_async
>> but it explicitly initializes the former and leaves compiler implicitly
>> initialize the later, that does not have an elegant look, solved by
>> explicitly initializing the later member as well that also makes @data
>> have full initialization.
>>
>> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
>> ---
>> IMO, this change still has a little bit of value as explained below:
>>
>> - Looks at below similar commit:
>> Commit: 8f45f5071ad2 ("gpu: host1x: Explicitly initialize host1x_info structures")
>>
>> - This change's initialization way is obvious better than
>>
>> struct device_attach_data data = {
>> 	.dev = dev,
>> 	.check_async = allow_async,
>> };
>>
>> which is better than current
>>
>> struct device_attach_data data = {
>> 	.dev = dev,
>> 	.check_async = allow_async,
>> 	.want_async = false,
>> };
> 
> Unlike host1x_info structure from commit 8f45f5071ad2 that you
> referenced, which sole purpose is to describe hardware, this is an
> internal structure in drivers/base/dd.c that mixes together scan
> parameters and internal state/result. The scan parameters are
> initialized explicitly to convey the exact request (i.e.  for given
> device we want to try to attach a driver synchronously, but also we
> might be interested in knowing if there is a matching driver that
> supports asynchronous probe), the state is not mentioned not to draw
> attention from the particulars of the request.
> 
> I'll leave this to Greg to decide if we wants to apply this change (I
> would not), but if you are doing this you need to make similar change
> for the 2nd instance of struct device_attach_data.

sorry, not follow you here

the 2nd instance in __device_attach_async_helper() is good as explained
below:
	struct device_attach_data data = {
		.dev		= dev,
		.check_async	= true,
		.want_async	= true,
	};

1) it is a normal usage to ONLY explicitly initialize these fields that
can't be implicitly initialized by compiler.

2) user does not care about @data.have_async, namely, it is NOT used
later to decide later logic for 2nd instance.

> 
> Thanks.
>