Hi,
On 1/31/20 2:39 PM, Benjamin Tissoires wrote:
Hi Hans,
On Fri, Jan 31, 2020 at 1:46 PM Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
__check_hid_generic is used to check if there is a driver, other then
the hid-generic driver, which wants to handle the hid-device, in which
case hid_generic_match() will return false so that the other driver can
bind.
But what if the other driver also has a match callback and that indicates
it does not want to handle the device? Then hid-generic should bind to it
and thus hid_generic_match() should NOT return false in that case.
This commit makes __check_hid_generic check if a matching driver has
a match callback and if it does makes its check this, so that
hid-generic will bind to devices which have a matching other driver,
but that other driver's match callback rejects the device.
I get that part, but I am not sure I'll remember this in 2 months time
when/if we need to extend the .match() in another driver.
I am especially worried about the potential circular calls where an
other driver decides to check on all the other drivers having a match
callback...
Could you add a little blurb either in hid-generic.c explaining the
logic, or (and) in hid.h where .match is defined?
Because now, we have 2 callers for .match(): hid-core and hid-generic
(and 2 is usually one too many :-/).
Ok, how about the following:
static int __check_hid_generic(struct device_driver *drv, void *data)
{
struct hid_driver *hdrv = to_hid_driver(drv);
struct hid_device *hdev = data;
if (hdrv == &hid_generic)
return 0;
if (!hid_match_device(hdev, hdrv))
return 0;
/*
* The purpose of looping over all drivers to see if one is a match
* for the hdev, is for hid-generic to NOT bind to any devices which
* have another, specialized, driver registerd. But in some cases that
* specialized driver might have a match callback itself, e.g. because
* it only wants to bind to a single USB interface of a device with
* multiple HID interfaces.
* So if another driver defines a match callback and that match
* callback returns false then hid-generic should still bind to the
* device and we should thus keep looping over the registered drivers.
*/
if (!hdrv->match)
return 1;
return hdrv->match(hdev, false);
}
?
Let me know if you like this then I'll send a v2 with this.
Regards,
Hans
