Re: [PATCH] ARM: dts: bcm283x: increase dwc2's RX FIFO size

[Pavel Hofman <pavel.hofman@ivitera.com>]

Dne 27. 05. 21 v 15:47 Stefan Wahren napsal(a):

>> I think I see the problem.
>>
>> IIUC the calculations and checks, all g-tx-fifo-size values +
>> g-rx-fifo-size + g-np-tx-fifo-size must not exceed total_fifo_size. My
>> RPi4 reports the total_fifo_size as 4080 (in
>> /sys/kernel/debug/usb/fe980000.usb/hw_params).
>>
>> Linux mainline
>> https://github.com/torvalds/linux/search?p=3&q=g-tx-fifo-size :
>>
>> The increase in value of g-rx-fifo-size exceeds the limit for the DTSI
>> files we patched:
>>
>> Both bcm283x-rpi-usb-peripheral.dtsi and bcm283x-rpi-usb-otg.dtsi:
>> 558 + 32 + 256 + 256 + 512 + 512 + 512 + 768 + 768 = 4174 > 4080
>>
>> while the sum with the previous value of 256 reached just 3872 < 4080.
>>
>>
>> The raspberrypi repo
>> https://github.com/raspberrypi/linux/search?q=g-tx-fifo-size :
>>
>> It has a different mix of the DTSI files
>> dwc2-overlay.dts
>> upstream-overlay.dts
>> upstream-pi4-overlay.dts
> yes these overlay files are vendor specific and doesn't exist in
> mainline. The upstream*dts were intended to "simulate" mainline
> behavior, but unfortunately differ in this case.
>>
>> all of which define
>> g-tx-fifo-size = <512 512 512 512 512 256 256>;
>>
>> Here the calculation holds:
>> 558 + 32 + 512 + 512 + 512 + 512 + 512 + 256 + 256 = 3662 < 4080
>>
>> My RPi4 uses one of these DTSIs, because my
>> /sys/kernel/debug/usb/fe980000.usb/params says:
>>
>> g_rx_fifo_size                : 558
>> g_np_tx_fifo_size             : 32
>> g_tx_fifo_size[0]             : 0
>> g_tx_fifo_size[1]             : 512
>> g_tx_fifo_size[2]             : 512
>> g_tx_fifo_size[3]             : 512
>> g_tx_fifo_size[4]             : 512
>> g_tx_fifo_size[5]             : 512
>> g_tx_fifo_size[6]             : 256
>> g_tx_fifo_size[7]             : 256
>>
>>
>> IIUC the tx_fifo values in bcm283x-rpi-usb-peripheral.dtsi and
>> bcm283x-rpi-usb-otg.dtsi files can be lowered to the values used and
>> tested (at least by me) in the RPi repo. But this is outside of my
>> knowledge, honestly I do not know what is the most appropriate
>> distribution of the remaining fifo space among the g_tx_fifo buffers.
>> Please can the RPi developers (Phil?) suggest a fix?
> 
> As author of the mainline bcm283x-rpi-usb-otg.dtsi i was trying to
> optimize the fifo sizes for EP 6 and 7. But i don't remember why. So my
> suggestion for a fix would be:
> 
> g-tx-fifo-size = <256 256 256 512 512 768 768>;
> 
> But i'm also unsure about the values.
> 

IIUC this code
https://github.com/torvalds/linux/blob/master/drivers/usb/dwc2/gadget.c#L4091
optimizes the FIFO assignment to endpoints. From that I would conclude
that correct values are specific for each use-case configuration of
endpoints. Maybe a varied selection (256, 512, 768) is more convenient
than just 256 and 512. I really do not know what use cases need what TX
fifo values.


BTW perhaps this comment
https://github.com/torvalds/linux/blob/master/drivers/usb/dwc2/gadget.c#L327
is a bit misleading since that code does not do the assignment, just
stores the size distribution to the DPTXFSIZN register, IIUC.

Best regards,

Pavel.