Re: [PATCH 4/4] pata_platform: Use 16-bit wide data transfer

[Alexander Shiyan <shc_work@mail.ru>]

On Mon, 25 Aug 2014 20:48:17 +0100
One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> wrote:

> On Mon, 25 Aug 2014 15:34:54 -0400
> Tejun Heo <tj@kernel.org> wrote:
> 
> > Hello,
> > 
> > On Sat, Aug 23, 2014 at 09:29:15PM +0400, Alexander Shiyan wrote:
> > > > Shouldn't we distinguish them instead of forcing 16bit transfer on
> > > > all?
> > > 
> > > I do not see any reason to distinguish. This embodiment can be used with
> > > 16-bit and 32-bit bus, and even for 64-bit ;)
> > 
> > Hmmm... we do care about doing 32bit when possible as there are cases
> > where PIO is the only data tarnsfer mode available 
> 
> Because some environments you get faster data transfers if you throw data
> at the controller in 32bit chunks. In some cases that's because the
> controller is clever about it and pipelining (eg some VLbus devices) in
> others for the simple reason that the external bus cycles are either
> 16bit or converted that way and the CPU executes a 32bit move followed by
> an add faster than 16bit/add/16bit/add.
> 
> (There are legacy memory mapped devices around where the fastest way
> to read them on an older x86 is to use the FPU to do 64bit reads, but some
> things should not be encouraged ;-) )

Seems my response to this message was lost in space ...
Just to repeat:

I did not understand a bit of the final solution...
I hope I have clearly explained the original problem, which was written for
this patch? This is not theory.

-- 
Alexander Shiyan <shc_work@mail.ru>