linux-kernel - Re: [PATCH v1 4/5] devres: Simplify devm_percpu

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Message-ID: <4ecbe215-6b73-48ea-8e8d-831e3682754c@quicinc.com>
Date: Thu, 4 Jul 2024 21:17:16 +0800
From: quic_zijuhu <quic_zijuhu@...cinc.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: <linux-kernel@...r.kernel.org>, <rafael@...nel.org>, <brgl@...ev.pl>,
        <madalin.bucur@....com>, <davem@...emloft.net>,
        <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH v1 4/5] devres: Simplify devm_percpu_match()
 implementation

On 7/4/2024 6:34 PM, Greg KH wrote:
> On Tue, Jul 02, 2024 at 10:51:53PM +0800, Zijun Hu wrote:
>> Simplify devm_percpu_match() implementation by removing redundant
>> conversions.
>>
>> Signed-off-by: Zijun Hu <quic_zijuhu@...cinc.com>
>> ---
>> Previous discussion link:
>> https://lore.kernel.org/lkml/1719496036-24642-1-git-send-email-quic_zijuhu@quicinc.com/
>>
>> Changes since the original one:
>>  - Select the simplier solution
>>
>>  drivers/base/devres.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/base/devres.c b/drivers/base/devres.c
>> index e9b0d94aeabd..2ad6dacb3472 100644
>> --- a/drivers/base/devres.c
>> +++ b/drivers/base/devres.c
>> @@ -1176,9 +1176,8 @@ static void devm_percpu_release(struct device *dev, void *pdata)
>>  
>>  static int devm_percpu_match(struct device *dev, void *data, void *p)
>>  {
>> -	struct devres *devr = container_of(data, struct devres, data);
>> -
>> -	return *(void **)devr->data == p;
>> +	/* @data is already and must be (void *)devr->data */
>> +	return *(void **)data == p;
> 
> The compiler output should be identical here, right?  And container_of()
yes, you are right.
> enforces the placement so I'd prefer the original here as a comment
> isn't going to enforce anything :)
> 
i would like to show 2 different points related to the comments below:

1) the comments is applicable for *ALL* kinds of devres match()s, and is
*NOT* specific to devm_percpu_match() and also does *NOT* enforce anything.

may i remove the comments?

2) the original implementation is *NOT* normative as explained below:
include/linux/device.h:
typedef int (*dr_match_t)(struct device *dev, void *res, void *match_data);
void *devres_find(struct device *dev, dr_release_t release,
		  dr_match_t match, void *match_data);

devres API users maybe need to write their match() functions, for
example, user of API devres_find(), but struct devres is a devres
internal implementation defined within devres.c and is *NOT* exposed to
API user by device.h, so API user should not use struct devres when
implement their devres match() normally.
but original devm_percpu_match() uses the struct devres.

> thanks,
> 
> greg k-h