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Message-ID: <20180705230602.GA25476@vmlxhi-102.adit-jv.com>
Date: Fri, 6 Jul 2018 01:06:02 +0200
From: Eugeniu Rosca <erosca@...adit-jv.com>
To: Ruslan Bilovol <ruslan.bilovol@...il.com>,
Julian Scheel <julian@...st.de>
CC: Eugeniu Rosca <roscaeugeniu@...il.com>,
Felipe Balbi <balbi@...nel.org>,
Felipe Balbi <felipe.balbi@...ux.intel.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
Takashi Iwai <tiwai@...e.de>,
Eugeniu Rosca <erosca@...adit-jv.com>
Subject: Re: [PATCHv2 3/3] usb: gadget: f_uac*: Support multiple sampling
rates
On Tue, Jul 03, 2018 at 01:29:54AM +0300, Ruslan Bilovol wrote:
> Hi guys,
>
> On Mon, Jul 2, 2018 at 7:30 PM, Eugeniu Rosca <erosca@...adit-jv.com> wrote:
> > Hi Julian,
> >
> > [CC:Takashi, since we are discussing sound-related parts of USB]
> >
> > On Mon, Jul 02, 2018 at 04:07:19PM +0200, Julian Scheel wrote:
> >> Hi Eugeniu,
> >>
> >> On 30.06.2018 20:16, Eugeniu Rosca wrote:
> >> > Would it be possible to revive the uac2 multiple sampling rate
> >> > patch-set [1] by rebasing it onto the most recent kernel? If you
> >> > don't have time for this, I could help you.
> >>
> >> I have this on my todo-list for a while now... In fact I fixed the build
> >> errors reported by the robot last year, but didn't had the time to
> >> verify all of it and push again.
> >> Still, I'd be happy to get this merged, so I'll try to check the state
> >> of this within the next days and either post to the list or get back to
> >> you if more work needs to be done.
> >
> > We've been living with an internally developed uac2 multiple rate
> > support since June 2015, initially written on top of v3.14. Due to
> > significant refactoring of uac2 driver brought by v4.13 commit [1], I
> > went through the comparison between the in-house implementation (which
> > no more applied cleanly to post-[1] vanilla) and your proposal from [2].
> >
>
> When Julian posted his patches, I've been working on UAC3 gadget
> implementation which I posted later [1]. While I originally tried to make
> UAC3 function to have same configfs files as UAC1/2, now, preparing
> UAC3 gadget patch I see it doesn't fit this approach, and patch
> "usb: gadget: f_uac*: Reduce code duplication" isn't applicable for UAC3
> case. Especially for channels configuration which in new spec can be
> done only through clusters descriptions, which makes configfs interface
> more complicated and not so straightforward as UAC1/2 have.
>
> I didn't finish my UAC3 gadget patch v2 yet, but if you can try to avoid
> adding patch "Reduce code duplication" or wait for a few weeks, when
> I'll post UAC3 patches, it would be great; so we will be able to take into
> account new spec as well.
>
> [1]: https://lkml.org/lkml/2017/11/6/1514
Hello Ruslan, hello Julian,
I took some time to study the implementations of existing uac drivers,
including uac3 v1 [1] and would like to share some thoughts with you.
My main thesis is that, w/o going too deep into the semantics and specs,
there is just a lot of code shared between the drivers. Why I am
pointing this out is because features like [2] and possibly a number of
other upcoming features which are agnostic on the exact UAC spec (just
like multiple rate support is) will need a copy-paste (and individual
maintenance) in every single UAC{1,2,3} driver.
To quantify the degree of similarity (the percentage of common
code), I took the uac2 driver as reference and compared it to uac1
and to uac3 implementations.
Some comments/assumptions:
- To get relevant diff output between the drivers, I needed to reorder
the functions some *.c files slightly (this already can be a source
of bugs, since contributors can't see the difference between the
drivers clearly).
- To highlight as much common code as possible, I needed to reorder
statements inside functions (some functions performing the same role
are doing things in slightly different order, which again can be
source of subtle bugs).
- I used v4.18-rc3, on top of which patch [1] applies cleanly.
- I only compared *.c code (functions and macros), not data structs.
- I ignored the differences in the names of local variables.
- I ignored the differences in the prints.
- I considered 'struct f_uac{1,2,3}_opts' identical, since they
really are.
- I ignored the difference between 'struct f_uac{1,2,3}' since they
can be easily unified.
- I ignored the values behind the 'UAC{1,2,3}_DEF_*' macros, since they
are not essential.
- Obviously, I ignored any whitespace difference.
- I paired the functions/macros by role.
- The actual % values are estimated *visually*, therefore might be not
precise (unless it is a 0% or 100%).
The results are drawn in the following two tables.
###### UAC2 vs UAC1
| uac2 | % | uac1 |
|------------------------|-----|------------------------|
| afunc_bind | 50 | f_audio_bind |
| afunc_unbind | 100 | f_audio_unbind |
| afunc_set_alt | 100 | f_audio_set_alt |
| afunc_get_alt | 100 | f_audio_get_alt |
| afunc_disable | 100 | f_audio_disable |
| in_rq_cur | 0 | - |
| in_rq_range | 0 | - |
| out_rq_cur | 0 | - |
| ac_rq_in | 0 | - |
| setup_rq_inf | 0 | - |
| afunc_setup | 50 | f_audio_setup |
| to_f_uac2_opts | 100 | to_f_uac1_opts |
| f_uac2_attr_release | 100 | f_uac1_attr_release |
| UAC2_ATTRIBUTE | 100 | UAC1_ATTRIBUTE |
| afunc_free_inst | 100 | f_audio_free_inst |
| afunc_alloc_inst | 100 | f_audio_alloc_inst |
| afunc_free | 100 | f_audio_free |
| afunc_alloc | 100 | f_audio_alloc |
| set_ep_max_packet_size | 0 | - |
| - | 0 | audio_get_endpoint_req |
| - | 0 | audio_set_endpoint_req |
###### UAC2 vs UAC3
| uac2 | % | uac3 |
|------------------------|-----|--------------------------|
| afunc_bind | 50 | f_audio_bind |
| afunc_unbind | 50 | f_audio_unbind |
| afunc_set_alt | 100 | f_audio_set_alt |
| afunc_get_alt | 100 | f_audio_get_alt |
| afunc_disable | 100 | f_audio_disable |
| in_rq_cur | 30 | in_rq_cur |
| in_rq_range | 30 | in_rq_range |
| out_rq_cur | 20 | out_rq_cur |
| ac_rq_in | 50 | ac_rq_in |
| setup_rq_inf | 90 | setup_rq_inf |
| afunc_setup | 100 | f_audio_setup |
| to_f_uac2_opts | 100 | to_f_uac3_opts |
| f_uac2_attr_release | 100 | f_uac3_attr_release |
| UAC2_ATTRIBUTE | 100 | UAC3_ATTRIBUTE |
| afunc_free_inst | 100 | f_audio_free_inst |
| afunc_alloc_inst | 100 | f_audio_alloc_inst |
| afunc_free | 100 | f_audio_free |
| afunc_alloc | 100 | f_audio_alloc |
| set_ep_max_packet_size | 100 | set_ep_max_packet_size |
| - | 0 | in_rq_hc_desc |
| - | 0 | uac3_copy_descriptors |
| - | 0 | alloc_fu_desc |
| - | 0 | build_cluster_descriptor |
| - | 0 | UAC3_ATTRIBUTE_CHMASK |
The message I wanted to share here is that, in my opinion, there is
really a lot of common code across UAC drivers. AFAIK features like
multiple sampling rate support really don't care about the exact UAC
spec, which means that w/o any attempt to reduce code duplication, we
would end up with duplicated (and diverging over time) implementations
of such features in several places.
Can I have your view on that?
Since you likely have more experience with uac* code, do you think is
feasible to isolate the common parts into a separate file?
Thanks,
Eugeniu.
[1] https://lkml.org/lkml/2017/11/6/1514 ("[PATCH 1/1]
usb: gadget: add USB Audio Device Class 3.0 gadget support")
[2] https://lkml.org/lkml/2017/6/30/276 ("[PATCHv2 0/3]
USB Audio Gadget: Support multiple sampling rates")
[3] https://lkml.org/lkml/2017/6/30/270 ("[PATCHv2 2/3]
usb: gadget: f_uac*: Reduce code duplication")
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