Re: [PATCH v2] dec: tulip: de4x5: Replace mdelay with usleep_range in de4x5_hw_init

[Jia-Ju Bai]

On 2018/4/12 10:21, arvindY wrote:
> On Thursday 12 April 2018 07:00 AM, Jia-Ju Bai wrote:
> > 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().
>
> James is right, You have added all usleep_range() during system 
> boot-up time.
> During boot-up system will run as single threaded. Where this change will
> not make much sense. System first priority is match the exact timing on
> each and every boot-up.

Hello, Arvind.
Thanks for your reply :)

I admit I am not familiar with this driver.
I did not know this driver is only loaded during system boot-up time,
I thought this driver can be loaded as a kernel module (like many 
drivers) after system booting.
After knowing this, I admit my patch is not proper, sorry...


Best wishes,
Jia-Ju Bai