Den 02.06.2020 13.46, skrev Noralf Trønnes:
Den 02.06.2020 04.32, skrev Alan Stern:
On Tue, Jun 02, 2020 at 12:12:07AM +0000, Peter Stuge wrote:
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The way I read composite_setup() after try_fun_setup: it calls f->setup() when available, and that can return < 0 to stall.
I expect that composite_setup() and thus f->setup() run when the SETUP packet has arrived, thus before the data packet arrives, and if composite_setup() stalls then the device/function should never see the data packet.
For an OUT transaction I think the host controller might still send the DATA packet, but the device controllers that I know don't make it visible to the application in that case.
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Are you guys interested in comments from other people who know more about the kernel and how it works with USB?
Absolutely, I want something thats works well in the kernel and doesn't look odd to kernel USB people.
Your messages have been far too long to go into in any detail, but I will address this one issue.
The USB protocol forbids a device from sending a STALL response to a SETUP packet. The only valid response is ACK. Thus, there is no way to prevent the host from sending its DATA packet for a control-OUT transfer.
A gadget driver can STALL in response to a control-OUT data packet, but only before it has seen the packet. Once the driver knows what the data packet contains, the gadget API doesn't provide any way to STALL the status stage. There has been a proposal to change the API to make this possible, but so far it hasn't gone forward.
This confirms what I have seen in the kernel and the reason I added a status request so I can know the result of the operation the device has performed.
I have a problem that I've encountered with this status request. In my first version the gadget would usb_ep_queue() the status value when the operation was done and as long as this happended within the host timeout (5s) everything worked fine.
Then I hit a 10s timeout in the gadget when performing a display modeset operation (wait on missing vblank). The result of this was that the host timed out and moved on. The gadget however didn't know that the host gave up, so it queued up the status value. The result of this was that all further requests from the host would time out. Do you know a solution to this? My work around is to just poll on the status request, which returns a value immediately, until there's a result. The udc driver I use is dwc2.
I have now tried this on a Beaglebone Black (musb udc driver) and it works just fine there (it displays an error message on the next request). So it has to be a dwc2 driver problem. I will try and chase down this problem when I get the time.
This means I don't need this status request polling in my host driver.
Noralf.