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Date: Tue, 20 Dec 2022 20:10:42 -0800 From: Guenter Roeck <groeck@...gle.com> To: Ruihai Zhou <zhouruihai@...qin.corp-partner.google.com> Cc: pmalani@...omium.org, bleung@...omium.org, groeck@...omium.org, knoxchiou@...omium.org, weishunc@...omium.org, chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org Subject: Re: [PATCH] platform/chrome: cros_ec_typec: deferred probe when typec count mismatch On Tue, Dec 20, 2022 at 6:10 PM Ruihai Zhou <zhouruihai@...qin.corp-partner.google.com> wrote: >> >> I think that is problematic. It might as well be that nports > >> EC_USB_PD_MAX_PORTS. >> > Yes, you're right. so we should consider it's a invalid argument and return -EINVAL if nports > EC_USB_PD_MAX_PORTS. right? Why ? While this would be a bug, it should hopefully be found early in development and never hit the field. I don't see a reason for changing the code. >> >> Is this really seen in the field ? The EC should never report a wrong >> (random) number of ports. If it is not ready, there should be _some_ >> indication that it isn't ready. Does it really report a more or less >> random number in this case ? > > Yes, I saw this on corsola board. The EC report a wrong number(not random), because corsola emulates HDMI MUX over the current > type-c mux stack. The ec has to fake a type-c port to pass the MUX info. But the task are not initiated on starting up, and increase the > type-c port counts after the tasks finished. In this case, I saw the typec->num_ports = 1, but the nports = 2, which will be probe failed and > block the HDMI mux function. > > I will send v2 patch, if nports > EC_USB_PD_MAX_PORTS, then return -EINVAL, but if nports > typec->num_ports, we consider wait a second > to ec task increase the type-c port counts if there're a HDMI DB attach, then return -EPROBE_DEFER The current code just reduces nports if it is larger than EC_USB_PD_MAX_PORTS. Again, I don't see a reason to change that. Anyway, I am not sure if the above will work reliably. I am not sure what "HDMI DB" refers to, but if it is an external connector its status could change anytime. In that situation, no amount of waiting would help. Either case, the EC on corsola should really not change the number of ports it supports. Either it is a constant that should not change, or it is dynamic and the EC would need to tell the host if the number of ports changes (up or down). Trying to fix this in cros_ec_typec without well defined protocol exchange with the EC is at best a kludge, but not a real solution. Thanks, Guenter
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