The existing UAC2 gadget has hard-coded bInterval=4 for HS/SS EP IN and EP OUT. This setting precludes using higher-bandwidth configurations successfully (the srate/chmask/ssize combination is accepted, but data are silently dropped). After discussing with John Keeping (https://lore.kernel.org/all/YcHIsR4AFaL9g6N2@donbot/) this series implements a compromise among the various requirements. Configfs params c_hs_bint/p_hs_bint between 1 to 4 set fixed bInterval. If the params are set to 0, maximum fitting max packet size and bInterval values for the required bandwidth are calculated and used, minimizing thus CPU load. The default value is 0, i.e. the automated calculation. It was chosen to simplify using the UAC2 gadget. Also, when existing installations require minimum bInterval to achieve minimum latency, they had to be modified in the code so far. Therefore it is assumed that having to set the parameters to fixed bInterval values would be no major difference to the current status. Additionally, the code warns if the required bandwidth exceeds the used max packet size/bInterval combination. The warning check if performed for FS too even if the current configuration ends up using HS/SS. The optimal solution would be preventing FS/HS/SS enumeration instead but such feature will require more patches and is not part of this series. The bInterval parameters are added to the legacy g_audio too as this module is still used in many existing UAC2 gadget tutorials and the added code is minimal. With regards, Pavel Hofman. Pavel Hofman (4): usb: gadget: f_uac2: add HS/SS bInterval to configfs usb: gadget: audio: Add HS/SS bInterval params for UAC2 usb: gadget: f_uac2: Optionally determine bInterval for HS and SS usb: gadget: f_uac2: Add speed names to bInterval dbg/warn .../ABI/testing/configfs-usb-gadget-uac2 | 2 + Documentation/usb/gadget-testing.rst | 2 + drivers/usb/gadget/function/f_uac2.c | 160 +++++++++++++----- drivers/usb/gadget/function/u_uac2.h | 4 + drivers/usb/gadget/legacy/audio.c | 15 ++ 5 files changed, 142 insertions(+), 41 deletions(-) -- 2.25.1
