netdev - Re: [PATCH] net: dsa: b53: Replace mdelay with msleep in b53_switch_reset

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Message-ID: <7d376874-8078-0252-ed7e-29392a519fc8@gmail.com>
Date:   Wed, 11 Apr 2018 09:19:04 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>,
        Phil Reid <preid@...ctromag.com.au>, andrew@...n.ch,
        vivien.didelot@...oirfairelinux.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: dsa: b53: Replace mdelay with msleep in
 b53_switch_reset_gpio

On 04/11/2018 12:14 AM, Jia-Ju Bai wrote:
> 
> 
> On 2018/4/11 13:30, Phil Reid wrote:
>> On 11/04/2018 09:51, Jia-Ju Bai wrote:
>>> b53_switch_reset_gpio() is never called in atomic context.
>>>
>>> The call chain ending up at b53_switch_reset_gpio() is:
>>> [1] b53_switch_reset_gpio() <- b53_switch_reset() <-
>>>     b53_reset_switch() <- b53_setup()
>>>
>>> b53_switch_reset_gpio() is set as ".setup" in struct dsa_switch_ops.
>>> This function is not called in atomic context.
>>>
>>> Despite never getting called from atomic context,
>>> b53_switch_reset_gpio()
>>> calls mdelay() to busily wait.
>>> This is not necessary and can be replaced with msleep() to
>>> avoid busy waiting.
>>>
>>> This is found by a static analysis tool named DCNS written by myself.
>>> And I also manually check it.
>>>
>>> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
>>> ---
>>>   drivers/net/dsa/b53/b53_common.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/dsa/b53/b53_common.c
>>> b/drivers/net/dsa/b53/b53_common.c
>>> index 274f367..e070ff6 100644
>>> --- a/drivers/net/dsa/b53/b53_common.c
>>> +++ b/drivers/net/dsa/b53/b53_common.c
>>> @@ -597,10 +597,10 @@ static void b53_switch_reset_gpio(struct
>>> b53_device *dev)
>>>       /* Reset sequence: RESET low(50ms)->high(20ms)
>>>        */
>>>       gpio_set_value(gpio, 0);
>>> -    mdelay(50);
>>> +    msleep(50);
>>>         gpio_set_value(gpio, 1);
>>> -    mdelay(20);
>>> +    msleep(20);
>>>         dev->current_page = 0xff;
>>>   }
>>>
>> Would that also imply gpio_set_value could be gpio_set_value_cansleep?
>>
> 
> Yes, I think gpio_set_value_cansleep() is okay here?
> Do I need to send a V2 patch to replace gpio_set_value()?

Yes, I would lump these two changes in the same patch since this is
effectively about solving sleeping vs. non sleeping operations.

Thanks!
-- 
Florian