On Mon, Jul 20, 2015 at 03:14:25PM +0200, Thierry Reding wrote: > * PGP Signed by an unknown key > > On Mon, Jul 20, 2015 at 12:59:41PM +0300, Peter De Schrijver wrote: > > On Fri, Jul 17, 2015 at 01:31:24PM +0200, Thierry Reding wrote: > > > > Old Signed by an unknown key > > > > > > 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: > > > > > > Old 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@xxxxxxxxxx>. > > > > > > > > > > > > Signed-off-by: Jon Hunter <jonathanh@xxxxxxxxxx> > > > > > > --- > > > > > > 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. > > > > > > > The peripheral driver doesn't know how long a request is queued in the memory > > controller. So it can't be responsible for ensuring this. > > Surely whenever the peripheral reports that the operation is done (be > that via some DMA controller interrupt or syncpoint increment) the > operation would have flushed from the memory controller. Drivers are > already supposed to make sure this is the case when they are removed or > suspended, so this would mean that we'd be adding all this code for no > real gain. > That highly depends on how the peripheral is implemented. I'm not sure we can assume things work this way. > It would also explain why we're currently not seeing any such problems. > I don't think we are doing agressive enough powergating today to see any problems. That might also mean we're just lucky. Cheers, Peter. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
