Hello! I would like to open a question about PCIe Warm Reset. Warm Reset of PCIe card is triggered by asserting PERST# signal and in most cases PERST# signal is controlled by GPIO.
Basically every native Linux PCIe controller driver is doing this Warm Reset of connected PCIe card during native driver initialization procedure. And now the important question is: How long should be PCIe card in Warm Reset state? After which timeout can be PERST# signal de-asserted by Linux controller driver? Lorenzo and Rob already expressed concerns [1] [2] that this Warm Reset timeout should not be driver specific and I agree with them. I have done investigation which timeout is using which native PCIe driver [3] and basically every driver is using different timeout. I have tried to find timeouts in PCIe specifications, I was not able to understand and deduce correct timeout value for Warm Reset from PCIe specifications. What I have found is written in my email [4]. Alex (as a "reset expert"), could you look at this issue? Or is there somebody else who understand PCIe specifications and PCIe diagrams to figure out what is the minimal timeout for de-asserting PERST# signal? There are still some issues with WiFi cards (e.g. Compex one) which sometimes do not appear on PCIe bus. And based on these "reset timeout differences" in Linux PCIe controller drivers, I suspect that it is not (only) the problems in WiFi cards but also in Linux PCIe controller drivers. In my email [3] I have written that I figured out that WLE1216 card needs to be in Warm Reset state for at least 10ms, otherwise card is not detected. [1] - https://lore.kernel.org/linux-pci/20200513115940.fiemtnxfqcyqo6ik@pali/ [2] - https://lore.kernel.org/linux-pci/20200507212002.GA32182@bogus/ [3] - https://lore.kernel.org/linux-pci/20200424092546.25p3hdtkehohe3xw@pali/ [4] - https://lore.kernel.org/linux-pci/20200430082245.xblvb7xeamm4e336@pali/
