Den 17.02.2020 11.32, skrev Neil Armstrong:
Hi,
On 16/02/2020 18:21, Noralf Trønnes wrote:
Hi,
A while back I had the idea to turn a Raspberry Pi Zero into a $5 USB to HDMI/SDTV/DSI/DPI display adapter.
Thinking about how to represent the display to the driver I realised that hardware use registers as API. And Linux does have a generic register abstraction: regmap. Furthermore this means that if I can do a regmap over USB implementation, it will be easy to do other functions like gpio, adc and others. After a few iterations trying to understand the USB subsystem and satisfying driver requirements, I now have something that looks promising.
I'm sending out an early version hoping to get feedback especially on the core parts that handles regmap and interrupts.
Overview:
USB Host : USB Device : -------------- : ---------------------------- | mfd: mud | : | f_mud | ---------- | Driver | -------------- : | | | Driver | ---------- | regmap-usb | : | (mud_regmap) | ---------- -------------- : ------------------
The idea is really like ARA's greybus, but much simpler ! Anyway nice idea, do you have good performance over USB2 and RPi's awful DWC2 gagdet controller ?
Not as good as I was hoping for. If I disable compression I'm getting 5 fps for a 1.5MB framebuffer (7800 kB/s):
$ modetest -M mud_drm -s 35:1024x768@RG16 -v setting mode 1024x768-60.00Hz@RG16 on connectors 35, crtc 33 freq: 5.07Hz
When I tried reading I discovered that it was almost 3 times faster than writing.
The zero gadget (loop testing) confirmed my findings:
Device: $ sudo modprobe g_zero [ 44.221890] zero gadget: Gadget Zero, version: Cinco de Mayo 2008 [ 44.221906] zero gadget: zero ready [ 60.751451] zero gadget: high-speed config #3: source/sink
Host:
$ sudo ~/testusb -a -t <n> -g 64 -s 16384 /dev/bus/usb/001/010 test 27, 107.230669 secs -> 1000 / 107 = 9MB/s /dev/bus/usb/001/010 test 28, 37.791292 secs -> 1000 / 37 = 27MB/s [73983.796552] usbtest 1-1.3:3.0: TEST 27: bulk write 1000Mbytes [74205.060204] usbtest 1-1.3:3.0: TEST 28: bulk read 1000Mbytes
$ sudo ~/testusb -a -t <n> -g 64 -s 16384 /dev/bus/usb/001/010 test 5, 107.421535 secs /dev/bus/usb/001/010 test 6, 38.189712 secs [74893.204170] usbtest 1-1.3:3.0: TEST 5: write 1000 sglists 64 entries of 16384 bytes [75012.592222] usbtest 1-1.3:3.0: TEST 6: read 1000 sglists 64 entries of 16384 bytes
I have tried Raspberry Pi1 and Pi4 as host (2 different controllers) and Pi Zero and Beaglebone Black as device, getting similar result.
I found this post having the same issue:
Re: Asymmetric speed results with testusb/usbtest/g_zero https://www.spinics.net/lists/linux-usb/msg100588.html
I haven't got a usb analyzer, but adding printk to dwc2_assign_and_init_hc() showed that IN interrupts were 2-3 ms apart but OUT interrupts were ~8 ms apart.
Noralf.