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

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Date:   Thu, 12 Apr 2018 09:49:33 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Florian Fainelli <f.fainelli@...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 2018/4/12 0:19, Florian Fainelli wrote:
> 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.

Okay, I have sent a V2 patch, and you can have a look :)


Best wishes,
Jia-Ju Bai