On Mon, 26 Sep 2022 07:49:55 -0400, Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx> wrote: > > On Sat, Sep 17, 2022 at 10:05:59AM +0100, Marc Zyngier wrote: > > Hi Lorenzo, > > > > On Fri, 09 Sep 2022 15:57:11 +0100, > > Lorenzo Pieralisi <lpieralisi@xxxxxxxxxx> wrote: > > > > > > [+Marc, Thomas - I can't merge this code without them reviewing it, > > > I am not sure at all you can mix the timer/IRQ code the way you do] > > > > > > On Thu, Aug 18, 2022 at 03:51:32PM +0200, Marek Behún wrote: > > > > From: Pali Rohár <pali@xxxxxxxxxx> > > > > > > > > Add support for Data Link Layer State Change in the emulated slot > > > > registers and hotplug interrupt via the emulated root bridge. > > > > > > > > This is mainly useful for when an error causes link down event. With > > > > this change, drivers can try recovery. > > > > > > > > Link down state change can be implemented because Aardvark supports Link > > > > Down event interrupt. Use it for signaling that Data Link Layer Link is > > > > not active anymore via Hot-Plug Interrupt on emulated root bridge. > > > > > > > > Link up interrupt is not available on Aardvark, but we check for whether > > > > link is up in the advk_pcie_link_up() function. By triggering Hot-Plug > > > > Interrupt from this function we achieve Link up event, so long as the > > > > function is called (which it is after probe and when rescanning). > > > > Although it is not ideal, it is better than nothing. > > > > > > So before even coming to the code review: this patch does two things. > > > > > > 1) It adds support for handling the Link down state > > > 2) It adds some code to emulate a Link-up event > > > > > > Now, for (2). IIUC you are adding code to make sure that an HP > > > event is triggered if advk_pcie_link_up() is called and it > > > detects a Link-down->Link-up transition, that has to be notified > > > through an HP event. > > > > > > If that's correct, you have to explain to me please what this is > > > actually achieving and a specific scenario where we want this to be > > > implemented, in fine details; then we add it to the commit log. > > > > > > That aside, the interaction of the timer and the IRQ domain code > > > must be reviewed by Marc and Thomas to make sure this is not > > > a gross violation of the respective subsystems usage. > > > > I don't see anything being a "gross violation" here, at least from an > > interrupt subsystem perspective. In a way, this is synthesising an > > interrupt on the back of some other event, and as long as the context > > is somehow appropriate (something that looks like an interrupt when > > pretending there is one), this should be OK. Other subsystems such as > > i2c GPIO expanders do similar things. > > Right, thanks. > > > The one thing I'm dubious about is the frequency of the timer. Asking > > for a poll of the link every jiffy is bound to be expensive, and it > > would be good to relax this as much as possible, specially on low-end > > HW such as this, where every cycle counts. It is always going to be a > > "best effort" thing, and the commit message doesn't say what's the > > actual grace period to handle this (the spec probably has one). > > AFAICS, the code does not poll the link. It sets a timer only if > the link is checked (eg upon PCI bus forced rescan or config access) > the link is up and it was down, to emulate a HP IRQ. I still find the timer frequency pretty high, but surely the authors of the code have worked out that this wasn't a problem. Thanks, M. -- Without deviation from the norm, progress is not possible.
