[PATCH V3 02/19] memory: tegra: Add MC flush support

[Peter De Schrijver]

On Fri, Jul 17, 2015 at 11:57:55AM +0200, Thierry Reding wrote:
> * PGP Signed by an unknown key
> 
> On Mon, Jul 13, 2015 at 01:39:40PM +0100, Jon Hunter wrote:
> > The Tegra memory controller implements a flush feature to flush pending
> > accesses and prevent further accesses from occurring. This feature is
> > used when powering down IP blocks to ensure the IP block is in a good
> > state. The flushes are organised by software groups and IP blocks are
> > assigned in hardware to the different software groups. Add helper
> > functions for requesting a handle to an MC flush for a given
> > software group and enabling/disabling the MC flush itself.
> > 
> > This is based upon a change by Vince Hsu <vinceh at nvidia.com>.
> > 
> > Signed-off-by: Jon Hunter <jonathanh at nvidia.com>
> > ---
> >  drivers/memory/tegra/mc.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++
> >  drivers/memory/tegra/mc.h |   2 +
> >  include/soc/tegra/mc.h    |  34 ++++++++++++++
> >  3 files changed, 146 insertions(+)
> 
> Do we know if this is actually necessary? I remember having a discussion
> with Arnd Bergmann a while ago, and the Linux driver model kind of
> assumes that by the time a device is disabled all outstanding accesses
> will have stopped.
> 
> Do we have a way to determine that this even makes a difference? Can we
> trigger a case where not doing this would cause breakage and see that
> adding this fixes that particular issue?
> 

Most likely it is. The memory controller can still be processing requests
when the peripheral domain is powergated. This would mean the response cannot
be delivered in that case. So we need to be sure there are no outstanding
requests before shutting down the domain.

Cheers,

Peter.