linux-kernel - Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)

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Message-ID: <5113C459.8000602@synopsys.com>
Date:	Thu, 7 Feb 2013 19:12:25 +0400
From:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Michal Simek <monstr@...str.eu>, Arnd Bergmann <arnd@...db.de>,
	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	"Geert Uytterhoeven" <geert@...ux-m68k.org>,
	<dahinds@...rs.sourceforge.net>
Subject: Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)_le16
 with generic iowrite(read)8/16(be)

On 02/07/2013 06:51 PM, Grant Likely wrote:
> On Thu, Feb 7, 2013 at 2:39 PM, Grant Likely <grant.likely@...retlab.ca> wrote:
>> On Wed, Feb 6, 2013 at 9:35 PM, Benjamin Herrenschmidt
>> <benh@...nel.crashing.org> wrote:
>>>>   In fact, the driver already knows about this and figures
>>>> out at runtime how the device is wired up to the bus. This is not the
>>>> problem.
>>>
>>> Except that this is very gross, especially when you observe that in the
>>> busted "big endian" case, it has to byteswap the bloody data port.
>>>
>>> So you end up having to do that gross hack with separate accessors for
>>> registers vs. data and not able to use the _rep variants, which also
>>> means that on platforms like ppc, you end up with a memory barrier on
>>> every access (or more), which is going to slow things down enormously.
>>
>> I don't see why the _rep variants aren't usable here. The only reason
>> I didn't use them when I wrote the driver in the first place was I was
>> a n00b kernel hacker and I didn't know they were there.
>
> The 8-bit variant is different though because the hardware requires
> pingponging between odd and even byte addresses to flush the fifo.
> Reading a data port even address (0x40) gives the least significant
> byte. Reading from an odd address (0x41) give the MSB and pops the
> data off the FIFO. So, yes, the _rep variant can't be used in 8-bit
> mode. It should still be fine in 16-bit.
>
> page 45: http://www.xilinx.com/support/documentation/data_sheets/ds080.pdf
>

Ok, so may I do a re-spin with these changes:
1. In "ace_in_be16" use "ioread16be"
2. In "ace_out_be16" use "iowrite16be"
3. In "ace_in_le16" use "ioread16"
4. In "ace_out_le16" use "iowrite16"
5. In "ace_datain_le16" use "ioread16_rep"
6. In "ace_dataout_le16" use "iowrite16_rep"

not sure about items for "ace_datain/out_be16" - what about _rep options 
here?

-Alexey
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