[+cc Heiner for ASPM conversation] On Tue, Oct 29, 2019 at 11:42:53AM +0100, Rafael J. Wysocki wrote: > On Tue, Oct 22, 2019 at 2:59 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > > [+cc Rafael, linux-pm, beginning of discussion at > > https://lore.kernel.org/r/d8574605f8e70f41ce1e88ccfb56b63c8f85e4df.1571638827.git.eswara.kota@xxxxxxxxxxxxxxx] > > > > On Tue, Oct 22, 2019 at 05:27:38PM +0800, Dilip Kota wrote: > > > On 10/22/2019 1:18 AM, Bjorn Helgaas wrote: > > > > On Mon, Oct 21, 2019 at 02:38:50PM +0100, Andrew Murray wrote: > > > > > On Mon, Oct 21, 2019 at 02:39:20PM +0800, Dilip Kota wrote: > > > > > > PCIe RC driver on Intel Gateway SoCs have a requirement > > > > > > of changing link width and speed on the fly. > > > > Please add more details about why this is needed. Since you're adding > > > > sysfs files, it sounds like it's not actually the *driver* that needs > > > > this; it's something in userspace? > > > > > We have use cases to change the link speed and width on the fly. > > > One is EMI check and other is power saving. Some battery backed > > > applications have to switch PCIe link from higher GEN to GEN1 and > > > width to x1. During the cases like external power supply got > > > disconnected or broken. Once external power supply is connected then > > > switch PCIe link to higher GEN and width. > > > > That sounds plausible, but of course nothing there is specific to the > > Intel Gateway, so we should implement this generically so it would > > work on all hardware. > > > > I'm not sure what the interface should look like -- should it be a > > low-level interface as you propose where userspace would have to > > identify each link of interest, or is there some system-wide > > power/performance knob that could tune all links? Cc'd Rafael and > > linux-pm in case they have ideas. > > Frankly, I need some time to think about this and, in case you are > wondering about whether or not it has been discussed with me already, > it hasn't. > > At this point I can only say that since we have an ASPM interface, > which IMO is not fantastic, it may be good to come up with a common > link management interface. The ASPM interface hasn't been merged yet, so if you have better ideas, now is the time. That one is definitely very low-level, partly because the first use case is working around defects in a specific device. Some sort of unification of link management does sound like a good idea. Bjorn
