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

[Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Fri, Jul 17, 2015 at 01:20:49PM +0300, Peter De Schrijver wrote:
> 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-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>.
> > > 
> > > Signed-off-by: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> > > ---
> > >  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.

My point is that that's the driver's responsibility anyway, hence making
the explicit flush unnecessary.

Thierry

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