Messages in this thread | | | From | Grant Likely <> | Date | Thu, 7 Feb 2013 14:51:49 +0000 | Subject | Re: [PATCH] drivers/block/xsysace - replace in(out)_8/in(out)_be16/in(out)_le16 with generic iowrite(read)8/16(be) |
| |
On Thu, Feb 7, 2013 at 2:39 PM, Grant Likely <grant.likely@secretlab.ca> wrote: > On Wed, Feb 6, 2013 at 9:35 PM, Benjamin Herrenschmidt > <benh@kernel.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
| |