linux-kernel - Re: [PATCH v2] dec: tulip: de4x5: Replace mdelay with usleep_range in de4x5_hw

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Message-ID: <8bac3385-97c6-fff1-17c6-11f5e98a039a@gmail.com>
Date:   Thu, 12 Apr 2018 09:30:32 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>,
        davem@...emloft.net, stephen@...workplumber.org,
        johannes.berg@...el.com, arvind.yadav.cs@...il.com,
        dhowells@...hat.com
Cc:     netdev@...r.kernel.org, linux-parisc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dec: tulip: de4x5: Replace mdelay with usleep_range in
 de4x5_hw_init



On 2018/4/12 0:16, James Bottomley wrote:
> On Wed, 2018-04-11 at 23:39 +0800, Jia-Ju Bai wrote:
>> de4x5_hw_init() is never called in atomic context.
>>
>> de4x5_hw_init() is only called by de4x5_pci_probe(), which is only
>> set as ".probe" in struct pci_driver.
>>
>> Despite never getting called from atomic context, de4x5_hw_init()
>> calls mdelay() to busily wait. This is not necessary and can be
>> replaced with usleep_range() to  avoid busy waiting.
>>
>> This is found by a static analysis tool named DCNS written by myself.
>> And I also manually check it.
> Did you actually test this?  The usual reason for wanting m/udelay is
> that the timing must be exact.  The driver is filled with mdelay()s for
> this reason.  The one you've picked on is in the init path so it won't
> affect the runtime in any way.  I also don't think we have the hrtimer
> machinery for usleep_range() to work properly on parisc, so I don't
> think the replacement works.
>
> James
>

Hello, James.
Thanks for your reply :)

I agree that usleep_range() here will not much affect the real execution 
of this driver.

But I think usleep_range() can more opportunity for other threads to use 
the CPU core to schedule during waiting.
That is why I detect mdelay() that can be replaced with msleep() or 
usleep_range().


Best wishes,
Jia-Ju Bai