Re: [PATCH 02/11] ARM: mach-shmobile: setup-r8a7740: add MERAM work-around

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi,

On Tuesday 22 May 2012 13:41:54 Paul Mundt wrote:
> On Mon, May 21, 2012 at 09:27:03PM -0700, Kuninori Morimoto wrote:
> > > If this exists within the MERAM register space, it should probably be
> > > handled in the MERAM driver itself. If this is all going to go to DT in
> > > the future it will be easy to to node to quirk matching then, but in the
> > > mean time we can match on CPU or machine types.
> > 
> > It is difficult.
> > A1 MERAM datasheet doesn't have detail explain / register map.
> 
> Yes, I'm familiar with the quality/reliability of our documentation.
> 
> > It just say
> > 
> > ------------------------------------------
> > Set the following register in the MERAM
> > 
> >  Register name: ICBR buffer control
> >  Address: H?$B!GFE95 0098
> >  Access size: 32 bits
> >  Initial value: H?$B!G0160 0168
> >  Setting value: H?$B!G0160 0164
> > 
> > ------------------------------------------
> > 
> > This work-around fixup MERAM memroy access erorr bug
> > (CEU/VIO6C/2D-DMAC/VCP1/VPU5F/JPU/DISP)
> > But we don't know what is these value.
> 
> The problem with doing these sorts of setting outside of the context of
> the MERAM driver is that the MERAM driver could just turn around and undo
> the work by setting whatever bit this workaround is clearing.
> 
> As long as this exists outside of the MERAM register map and we don't have
> to worry about the MERAM driver touching these values then having it as a
> board-specific thing is probably fine. If it falls within the MERAM mapping
> somewhere then the MERAM driver really should be dealing with it (or we can
> set it as a board-specific thing when the MERAM driver isn't being used),
> even if it is a magic value for the given CPU.

I agree. 0xFE950098 is outside of the MERAM registers address space (at least 
in the SH7372 datasheet I have). I'm thus fine with setting the register in 
board code.

> The main thing is avoiding subtle hard to debug problems where the board
> config workarounds are inadvertently trampled later on.

-- 
Regards,

Laurent Pinchart