-----Original Message----- From: Alan Stern [mailto:stern@xxxxxxxxxxxxxxxxxxx] Sent: Monday, April 17, 2006 7:45 PM To: Kaustav Majumdar (WT01 - Semiconductors & Consumer Electronics) Cc: linux-usb-devel@xxxxxxxxxxxxxxxxxxxxx; linux-pm@xxxxxxxxxxxxxx Subject: Re: [linux-pm] Behavior of PCMCIA based HCD in the event of SUSPEND On Mon, 17 Apr 2006 kaustav.majumdar@xxxxxxxxx wrote: >> Hi all, >> >> I have the following queries regarding the power management on a PCMCIA >> based USB host controller driver. >> >> 1. The SUSPEND event in the PCMCIA client driver is handled in the >> following way: >> >> In the PCMCIA layer, on a SUSPEND event, the socket layer powers off the >> card. As the USB framework behavior is not allowed to suspend if lower >> nodes are not already suspended, we assume that the correct behavior for >> the above case should be to shut down the Host Controller. >> I want to confirm whether the assumed behavior is ok or should the >> behavior be something else? > The HCD's behavior should be to suspend the host controller, with the > understanding that factors beyond the HCD's control (such as the > behavior of the PCMCIA client driver) may cause the host controller to be > shut down entirely. The HCD should not shut down the host controller > during a suspend event. As per my understanding, the Host Controller can be suspended only if all the child devices are already suspended. If they are not then suspension of HC will fail. Also the PCMCIA subsystem's behavior is to power off the socket irrespective of whether the PCMCIA client driver has successfully handled the SUSPEND event or not. So if the child devices of HC are not suspended and PCMCIA subsystem will get a SUSPEND event (may be initiated by some user space tool through /sys) then there is a possibility of HC being in operational state (from driver perspective) but the PC Card itself not powered - a chaos I think. >> 2. And if the correct behavior is what we had assumed, then to implement >> that we call usb_remove_hcd from the PCMCIA client driver. Is this the >> correct way to do so? > No. The PCMCIA client driver should not make any assumptions about its > clients. All it should do is check that all the clients have been > suspended already before allowing itself to be suspended. First of all, is there any way to check the state of all the clients from inside the PCMCIA client driver? Please suggest. Secondly, what should we do in the PCMCIA client driver if the check fails? Here point to be noted is, as already mentioned, the PCMCIA socket will be powered off. >> The reason for the question is it can happen that after suspending the >> card, before resume card may be manually removed. In that case, there is >> a possibility of usb_remove_hcd being called twice consecutively which >> can cause error. >> Please suggest if any better way of implementing the above. > The PCMCIA client driver should not call usb_remove_hcd at all. Only a > USB host controller driver is allowed to call that routine. Actually we are not calling usb_remove_hcd directly. We are implementing the HCD module and there we have a function which is exported. From PCMCIA client driver we call this function, which in turn calls usb_remove_hcd. I am not sure whether this will be ok or not. Thank you, With regards, Kaustav > Alan Stern
