[PATCH v3 42/46] usb: gadget: move ep_matches() from epautoconf to udc-core

[Robert Baldyga]

On 07/26/2015 05:14 PM, Alan Stern wrote:
> On Sun, 26 Jul 2015, Petr Cvek wrote:
>
>> What about higher speeds (not relevant on PXA, but ep_matches() is
>> called from usb_ep_autoconfig_ss() )? According to
>>
>> 	http://wiki.osdev.org/Universal_Serial_Bus#Maximum_Data_Payload_Size_2
>>
>> High speed INT endpoint has a maximum data payload 1024 B and BULK
>> only 512 B (are other attributes of the data phase similar?). What
>> about superspeed?
>
> It's true that high speed interrupt endpoints can have higher maxpacket
> values than bulk endpoints.  But this is okay, since ep_matches()
> checks that the hardware maxpacket value is at least as large as the
> value in the descriptor:
>
> 		if (ep->maxpacket_limit < max)
> 			return 0;
>
>>>> * modprobe g_serial use_acm=1 n_ports=1
>>>> * original version of ep_matches() (returns bulk and int)
>>>> * compatible EP configuration/definition for UDC side http://lxr.free-electrons.com/source/drivers/usb/gadget/udc/pxa27x_udc.c#L2352
>>>> 	USB_EP_CTRL,
>>>> 	USB_EP_OUT_BULK(1),
>>>> 	USB_EP_IN_BULK(2),
>>>> 	USB_EP_IN_ISO(3),
>>>> 	USB_EP_OUT_ISO(4),
>>>> 	USB_EP_IN_INT(5),
>>>> * modified EP configuration for UDC side (just changed EP3 ISO to BULK, so there is one free BULK)
>>>> 	USB_EP_CTRL,
>>>> 	USB_EP_OUT_BULK(1),
>>>> 	USB_EP_IN_BULK(2),
>>>> 	USB_EP_IN_BULK(3),	//change
>>>> 	USB_EP_OUT_ISO(4),
>>>> 	USB_EP_IN_INT(5),
>>>>
>>>> ===results===
>>>> * original configuration is OK, all endpoints are found (in order ep2in-bulk, ep1out-bulk, ep3in-int), INT notification seems to work
>>>
>>> I don't understand.  Above you said that the EP definition in the UDC
>>> is USB_EP_IN_ISO(3).  So how can you end up with ep3in-int?  int != ISO.
>>> You should have ended up with the third endpoint being ep5in-int,
>>> because ep_matches() doesn't allow an isochronous to match a request
>>> for an interrupt endpoint.
>>
>> I have changed definition of ISO to BULK only to accomplish minimal
>> change of driver code (for my demonstration free BULK must be defined
>> before INT - inserting new EP would require to reindex all next EPs
>> and modifying links from PXA side endpoints). The USB_EP_IN_ISO(3) is
>> just "unused" endpoint.
>
> This doesn't answer my question.  I was asking about the original
> configuration, not your changed configuration.  You wrote:
>
>> * original configuration is OK, all endpoints are found (in order
>> ep2in-bulk, ep1out-bulk, ep3in-int), INT notification seems to work
>
> But that isn't possible, because in the original configuration ep3in is
> iso, not int.  Did you intend to write "ep5in-int" rather than
> "ep3in-int"?
>
>>>> * modified configuration fails:
>>>>
>>>> 	[ 4259.609088] pxa27x-udc pxa27x-udc: ep15:pxa_ep_enable: type mismatch
>>>>
>>>> by this condition:
>>>>
>>>> 	http://lxr.free-electrons.com/source/drivers/usb/gadget/udc/pxa27x_udc.c#L1416
>>>>
>>>> because ep_matches() returns BULK.
>>>
>>> Okay, that's a problem in pxa27x-udc.  Why does it insist on an exact
>>> match between the hardware endpoint type and the type contained in the
>>> descriptor?  It should accept an interrupt descriptor if the hardware
>>> type is bulk.
>>
>> Hmm, making BULK EP equivalent with INT EP (when INT is requested)
>> would made debugging (there is special bitfield in the config
>> registers) and configuration preset (not anymore unordered set, but
>> definition in the specific sequence) hell. But in other ways it can
>> be OK (specification does not say that using EP marked INT as BULK
>> will fail).
>
> This business about using bulk endpoints in place of interrupt
> endpoints goes back to the days when most UDCs had a very limited
> selection of endpoints.  The idea was that a gadget could work even if
> there weren't enough interrupt endpoints in the hardware, provided
> there were extra bulk endpoints.
>
>> I think optimal idea is custom matcher function. It would eliminate
>> codes for superspeed checking on SoC which known only fullspeed ;-).
>
> Wuldn't it also mean duplicating a lot of code?  Each custom matcher
> function would essentially have to include most of ep_matches().

I have solved this problem making ep_matches() public helper function, 
so we can avoid duplicated code. BTW this entire discussion is in reply 
to my patch doing this :)

>
>> P.S. I did a basic research where UDCs differ between BULK and INT
>> handling (just searching for usb_endpoint_type(), USB_ENDPOINT_XFER_*
>> and usb_endpoint_xfer_*() so it returned BULK on a software side -
>> irrelevant):
>> 	r8a66597-udc.c (using different constants, dedicated structure entries)
>> 	m66592-udc.c (same as r8a66597-udc.c)
>> 	dummy_hcd.c (well it is only dummy, says "bulk is OK" for INT, but has different matching rules for HS BULK and INT)
>> 	atmel_usba_udc.c (only by write of some flag)
>> 	net2272.c (fails with BULK, USB_SPEED_HIGH and maxpacket != 512)
>> 	at91_udc.c (only BULK is only OK with 8,16,32,64 values)
>> 	pxa25x_udc.c (setting one flag when hw (?) endpoint is BULK and another if nonBULK, INT FIFO size defined as 8, BULK FIFO as 64)
>> 	net2280.c (INT path has erratum, different maxpacket matching)
>> 	pxa27x_udc.h (INT_FIFO_SIZE defined as 16B, BULK_FIFO_SIZE defined as 64B)
>> 	mv_udc_core.c (different codepath)
>> 	gr_udc.c (using mode of endpoint to print messages and register setting)
>> 	fsl_qe_udc.c (different maxpacket sizes for highspeed)
>> 	udc-xilinx.c (maching of different maxpacket sizes)
>> 	omap_udc.c (maxpacket size definitions)
>
> The fact that bulk and interrupt are handled differently doesn't mean
> that you aren't allowed to allocate a bulk endpoint when the gadget
> driver quested an interrupt endpoint.
>
> On the other hand, it certainly would be better to do this only when no
> interrupt endpoints remain available.  As it stands now,
> usb_ep_autoconfig_ss() uses the first match it finds even if there is a
> better match later on.