On Fri, Nov 08, 2019 at 04:30:27PM +0900, Kunihiko Hayashi wrote: > Hi Andrew, > +CC Kishon > > On Thu, 7 Nov 2019 12:46:17 +0000 <andrew.murray@xxxxxxx> wrote: > > > On Thu, Nov 07, 2019 at 08:52:39PM +0900, Kunihiko Hayashi wrote: > > > Hi Andrew, > > > Thank you for your comments. > > > > > > On Thu, 7 Nov 2019 10:02:08 +0000 <andrew.murray@xxxxxxx> wrote: > > > > > > > On Thu, Nov 07, 2019 at 01:58:15PM +0900, Kunihiko Hayashi wrote: > > > > > When PERST# is asserted once, EP configuration will be initialized. > > > > > > > > I don't quite understand this - does the EP/RC mode depend on how often > > > > PERST# is toggled? > > > > > > I think of connecting this RC controller and EP based on `Linux PCI > > > endpoint framework' in another machine. > > > > > > While this RC driver is probing, the EP driver might be also probing and > > > configurating itself using configfs. If PERST# is toggled after the EP > > > has done its configuration, this configuration will be lost. > > > > > > I expect that the EP configurates after RC has toggled PERST#, however, > > > there is no way to synchronize both of them. > > > > > > > OK I understand where you are coming from now. Please ensure the commit > > message gives this rationale. > > I'll explain about that in the commit message next. > > > However, If I understand correctly, doesn't your solution only work some > > of the time? What happens if you boot both machines at the same time, > > and PERST# isn't asserted prior to the kernel booting? > > I think it contains an annoying problem. > > If PERST# isn't toggled prior to the kernel booting, PERST# remains asserted > and the RC driver can't access PCI bus. > > As a result, this patch works and deasserts PERST# (and EP configuration will > be lost). So boot sequence needs to include deasserting PERST#. > > > The only way you can ensure the EP is started after the RC is initialised > > is to start the EP after the RC is initialised. > > Yes, it's the only soution for now. > > > I'm not sure what the solution is here, but it feels like this approach > > only partially solves it. > > Surely relying on outside of the driver doesn't seem to be a complete solution. > > If there is the way that `Linux PCI endpoint framework' assumes, > I'd like to follow it, however, I can't find the other way. Indeed, this must be a common problem - many host controller drivers in the tree toggle perst on start up. Keen for any feedback from Kishon on this. Thanks, Andrew Murray > > Thank you, > > --- > Best Regards, > Kunihiko Hayashi > >
