On 8/3/22 16:55, Luiz Augusto von Dentz wrote: > Hi Vicki, > > On Wed, Aug 3, 2022 at 4:07 PM Vicki Pfau <vi@xxxxxxxxxxx> wrote: >> >> Though a 512 byte report map size seems plenty large, there exist some devices >> (e.g. Brydge W-Touch) that send larger reports. There is no protocol-defined >> maximum size so doubling the maximum size is safe, and should hopefully fix >> most real-world failures. >> --- >> profiles/input/hog-lib.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/profiles/input/hog-lib.c b/profiles/input/hog-lib.c >> index 4a9c60185..9f3eb428c 100644 >> --- a/profiles/input/hog-lib.c >> +++ b/profiles/input/hog-lib.c >> @@ -64,7 +64,7 @@ >> #define HOG_PROTO_MODE_BOOT 0 >> #define HOG_PROTO_MODE_REPORT 1 >> >> -#define HOG_REPORT_MAP_MAX_SIZE 512 >> +#define HOG_REPORT_MAP_MAX_SIZE 1024 >> #define HID_INFO_SIZE 4 >> #define ATT_NOTIFICATION_HEADER_SIZE 3 > > Afaik 512 is the maximum length an attribute can have even when using > read long procedure: > > BLUETOOTH CORE SPECIFICATION Version 5.3 | Vol 3, Part F > page 1416: > > The maximum length of an attribute value shall be 512 octets. > > And > > BLUETOOTH SPECIFICATION > HID Service Specification > Page 16 of 26 > > 2.6.1 Report Map Characteristic Behavior > The GATT Read Characteristic Value or Read Long Characteristic Values sub- > procedures are used to read the Report Map characteristic value. > The length of the Report Map characteristic value is limited to 512 octets. > > So I believe the device is not compliant and very likely needs to have > multiple instances of HID Service instead of combining everything in a > single instance. > >> -- >> 2.37.1 >> > > Ah, that's strange. I looked through the spec but didn't see those. That said, while the device may be non-compliant, the device is on the market and I doubt I could get them to update the firmware as a random third party. It works on Windows, so clearly Windows doesn't have a problem with its noncompliance. So this raises the question, how should Linux handle non-compliant hardware, especially when it could easily be made to work just by bending the rules in this one instance? I can absolutely change the commit message since it's erroneous, but the question then comes down to how should it be handled at all.
