On 17/07/15 12:31, Thierry Reding wrote: > * PGP 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. I see your point and it is interesting. The trouble is that we would need to test every memory client in every power domain to prove this. So I don't think that is a trivial thing to do. Furthermore, looking at what we have done in kernel used for android products (which probably stress PM the most) this is done and so I don't know of any shipping product that stresses PM that does not do this. May be someone else might. I personally would not be comfortable removing this without testing, but as I mentioned it is not a trivial thing to test correctly. However, I will let you and the other maintainers decide what's best here. Jon -- 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
