netdev - Re: [net v2 3/8] net/fsl_pq_mdio: Replace spin_event

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Date:	Tue, 7 Oct 2014 15:16:10 +0300
From:	Claudiu Manoil <claudiu.manoil@...escale.com>
To:	David Laight <David.Laight@...LAB.COM>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"David S. Miller" <davem@...emloft.net>,
	Xiubo Li <Li.Xiubo@...escale.com>,
	Shruti Kanetkar <Shruti@...escale.com>,
	"Kim Phillips" <kim.phillips@...escale.com>
Subject: Re: [net v2 3/8] net/fsl_pq_mdio: Replace spin_event_timeout() with
 arch independent

On 10/7/2014 11:12 AM, David Laight wrote:
> From: netdev-owner@...r.kernel.
>> spin_event_timeout() is PPC dependent, use an arch independent
>> equivalent instead.
>
> I think you should white a local function/#define that expands to spin_event_timeout()
> on ppc and to the code below you are substituting on other architectures.
>
>>   	/* Wait for the transaction to finish */
>> -	status = spin_event_timeout(!(ioread32be(&regs->miimind) &
>> -				    MIIMIND_BUSY), MII_TIMEOUT, 0);
>> +	timeout = MII_TIMEOUT;
>> +	while ((ioread32be(&regs->miimind) & MIIMIND_BUSY) && timeout) {
>> +		cpu_relax();
>> +		timeout--;
>> +	}
>
> 	David
>
>
>

Hi David,

This point is debatable. Still better than adding a new local function 
would be to provide an implementation for spin_even_timeout() for ARM.
But it is not the place of the ethernet driver to provide an 
implementation of spin_event_timeout() on ARM.
Instead, I opted to simplify the busy wait/ timeout mechanism
in the driver using a simple and arch independent implementation 
replacing the PPC specific spin_event_timeout().  This timeout 
implementation, open-coded as a while() loop, is commonly used by other 
drivers too and I think that for this particular driver (fsl_pq_mdio) it 
is good enough to do the job, while keeping the code simple and 
portable.  It may not be as precise as spin_event_timeout() on PPC, but 
good enough.

Thanks,
Claudiu

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