linux-kernel - Re: [PATCH 01/48] clk: at91: replace usleep() by udelay() calls

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Date:	Tue, 14 Jun 2016 18:18:20 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Afzal Mohammed <afzal.mohd.ma@...il.com>
Cc:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Arnd Bergmann <arnd@...db.de>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	linux-kernel@...r.kernel.org,
	Cyrille Pitchen <cyrille.pitchen@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 01/48] clk: at91: replace usleep() by udelay() calls

On Tue, 14 Jun 2016 21:35:17 +0530
Afzal Mohammed <afzal.mohd.ma@...il.com> wrote:

> Hi,
> 
> On Mon, Jun 13, 2016 at 05:24:09PM +0200, Alexandre Belloni wrote:
> > On 11/06/2016 at 00:30:36 +0200, Arnd Bergmann wrote :  
> 
> > > Does this have to be called that early? It seems wasteful to always
> > > call udelay() here, when these are functions that are normally
> > > allowed to sleep.  
> 
> > So I've tested it and something like that would work:
> > 
> > 	if (system_state < SYSTEM_RUNNING)
> > 		udelay(osc->startup_usec);
> > 	else
> > 		usleep_range(osc->startup_usec, osc->startup_usec + 1);
> > 
> > But I'm afraid it would be the first driver to actually do something
> > like that (however, it is already the only driver trying to sleep).   
> 
> tglx has suggested to modify clock core to handle a somewhat similar
> kind of scenario (probably should work here too) and avoid driver
> changes,
> 
> http://lkml.kernel.org/r/alpine.DEB.2.11.1606061448010.28031@nanos

Oh, interesting. Definitely a better solution than this custom check.


-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com