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

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Date:	Tue, 12 Feb 2013 18:02:58 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	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)

2013/2/7 Grant Likely <grant.likely@...retlab.ca>:
> On Thu, Feb 7, 2013 at 3:12 PM, Alexey Brodkin
> <Alexey.Brodkin@...opsys.com> wrote:
>> 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:
>
> There are two things here. 1) changing the accessors used. 2)
> switching the endianess as a bug fix. Any changes to the endian access
> should be a separate patch which a description of what is needed.
>
>> 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"
>
> Yes
>
>> 5. In "ace_datain_le16" use "ioread16_rep"
>> 6. In "ace_dataout_le16" use "iowrite16_rep"
>
> Maybe. In a separate patch. Hmmm... I guess there isn't an
> ioread16be_rep variant. Oh well. Check first with Michal on LE
> microblaze before making the change. If it doesn't work for him the
> more understanding is needed. I was pretty sure the LE variant already
> worked.

Sorry it took me some time to get 16bit LE to work for test but here
are test results.

I have tested it on ppc BE, Microblaze BE and Microblaze LE systems
and surprisingly on all of them only ace_reg_le16_ops are used.

But on Microblaze LE is necessary to use different datain/out_le16
functions as below
which are also not compatible with Microblaze and PPC BE.

diff --git a/drivers/block/xsysace.c b/drivers/block/xsysace.c
index bbad046..8dd192c 100644
--- a/drivers/block/xsysace.c
+++ b/drivers/block/xsysace.c
@@ -314,7 +314,7 @@ static void ace_datain_le16(struct ace_device *ace)
        int i = ACE_FIFO_SIZE / 2;
        u16 *dst = ace->data_ptr;
        while (i--)
-               *dst++ = ioread16be(ace->baseaddr + 0x40);
+               *dst++ = ioread16(ace->baseaddr + 0x40);
        ace->data_ptr = dst;
 }

@@ -323,7 +323,7 @@ static void ace_dataout_le16(struct ace_device *ace)
        int i = ACE_FIFO_SIZE / 2;
        u16 *src = ace->data_ptr;
        while (i--)
-               iowrite16be(*src++, ace->baseaddr + 0x40);
+               iowrite16(*src++, ace->baseaddr + 0x40);
        ace->data_ptr = src;
 }

Grant: How did you tested BE mode? It is fpga it means you can switch
some connections
and it could work.

Thanks,
Michal


-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel - Microblaze cpu - http://www.monstr.eu/fdt/
Maintainer of Linux kernel - Xilinx Zynq ARM architecture
Microblaze U-BOOT custodian and responsible for u-boot arm zynq platform
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