linux-kernel - Re: [PATCH 1/2] [IDE] Platform IDE driver (was: MMIO IDE driver)

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Date:	Wed, 25 Jul 2007 14:05:56 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
CC:	Vitaly Bordug <vitb@...nel.crashing.org>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org
Subject: Re: [PATCH 1/2] [IDE] Platform IDE driver (was: MMIO IDE driver)

Sergei Shtylyov wrote:
>>+	hwif->hw.io_ports[IDE_DATA_OFFSET] = port;
>>+
>>+	port += (1 << pdata->ioport_shift);
>>+	for (i = IDE_ERROR_OFFSET; i <= IDE_STATUS_OFFSET;
>>+	     i++, port += (1 << pdata->ioport_shift))
> 
> 
>     Looks like shift doesn't buy as anything, why not just use stride?

It doesn't buy us anything in here, but it's conceivable that someone 
may want to write a driver that uses a shift in the I/O accessor rather 
than an array of port offsets, and it's easier to convert a shift to a 
stride than the other way around (not all architectures have an 
equivalent of the cntlzw innstruction, and shift makes it clear that the 
stride must be power-of-two).  Plus, using shift is consistent with what 
we do on ns16550.

-Scott
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