[Gta04-owner] Small update to 3.7-gta04 kernel: faster wifi. Issue #488

[NeilBrown]

On Sat, 19 Oct 2013 09:51:59 +0200 "Dr. H. Nikolaus Schaller"
<hns at goldelico.com> wrote:

> Hi,
> 
> Am 19.10.2013 um 01:56 schrieb NeilBrown:
> 
> > On Fri, 18 Oct 2013 13:47:43 +0200 "Dr. H. Nikolaus Schaller"
> > <hns at goldelico.com> wrote:
> > 
> >> 
> >> Am 18.10.2013 um 13:17 schrieb NeilBrown:
> >> 
> >>> On Fri, 18 Oct 2013 12:00:57 +0200 "Dr. H. Nikolaus Schaller"
> >>> <hns at goldelico.com> wrote:
> >>> 
> >>>> Hi Neil,
> >>>> 
> >>>> Am 18.10.2013 um 11:44 schrieb NeilBrown:
> >>>> 
> >>>>> 
> >>>>> I've just pushed out a small update to 3.7-gta04.
> >>>>> 
> >>>>> This update adds support for the IRQ line from SDIO cards, such as the wifi
> >>>>> in the gta04.
> >>>>> This allows the wifi to go faster.
> >>>>> With polling (the old behaviour) I get about 1Mb/sec
> >>>>> With Interupts enabled and polling disabled I get about 4Mb/sec.
> >>>>> If I have interrupts *and* polling (which admittedly is a strange
> >>>>> config to even try) I get 5Mb/sec on my 800MHz board, and 6Mb/sec on
> >>>>> my 1GHz board.
> >>>> 
> >>>> That is good news for Issue #488 [1].
> >>>> 
> >>>>> So the code currently does both.  It is a bit of a hack (and not the only
> >>>>> hack) but it works OK for now.
> >>>>> 
> >>>>> This is will well short of the 40Mb/sec my notebook gets!
> >>>>> So it is an improvement, but not as much as I had hoped.
> >>>> 
> >>>> Does you patch also work for 3.12 or does it need (additional) hacks?
> >>>> 
> >>>> Or has anyone already done speed tests with 3.12 showing if it is
> >>>> really needed or not?
> >>> 
> >>> There is a 3.12 patch in my 'mainline' branch.
> >>> 
> >>> http://git.neil.brown.name/git?p=gta04.git;a=commitdiff;h=ad39271dc470f4c1ce048e58e4d137b37d5ff808
> >>> 
> >>> 
> >>> There were patches on the omap list recently:
> >>> https://lkml.org/lkml/2013/10/5/36
> >>> 
> >>> but they don't work for me.
> >>> 
> >>>> 
> >>>> BTW: the MMC1 interface (SD card) is running with ca. 19 MByte/s
> >>>> (which fits to the 25 MHz clock and 8 data bits parallel bus).
> >>> 
> >>> Isn't it a 4bit bus between the OMAP and the WIFI?
> >> 
> >> Yes, but that should still allow for ~ 9 MByte/s = 72 Mbit/s bandwidth.
> >> 
> >> So I wonder why we get the high data rate at the MMC1 interface
> >> without IRQ patches, but not at MMC2 (with SDIO and Libertas).
> > 
> > I don't think you can really compare memory card access with SDIO access.
> > The former is synchronous - the host is in complete control.
> > The later is asynchronous.  The SDIO card (wifi chip) does a lot of the work
> > and interrupts the host when there is something for it to do.
> 
> Ah, I see. So the theoretically available speed of the interface is not reached 
> if the CPU code is slow...
> 
> > 
> > My guess is that there is some latency between the IRQ line being asserted,
> > and the libertas driver handing it.
> > That could explain the better throughput in the 1GHz board: if the latency is
> > causes by lots of instructions being executed, they would execute faster on
> > the faster board.
> > 
> > Looking at the code I don't see anything obvious, but I'm not really sure
> > what to look for.
> > 
> 
> I have found that Andreas Kemnade already had shared a patch for 3.5-rc2
> quite a while ago. I may have noticed it back then and assumed that it is part
> of 3.7 and therefore became automagically part of 3.12. What a pity that we
> don't work on a single repository and the same kernel version until recently...
> 
> Here was his patch:
> 
> http://lists.goldelico.com/pipermail/gta04-owner/2012-June/002483.html

So he did.  I wonder why I missed that.

> 
> And he mentioned in a follow-up that the speed throttle may also be related
> to power/fclk management. This appears to be very similar to your patch so
> that I wonder if you may have based yours on his code? Then, we should
> mention Andreas in the Signed-off: note as well.

Only similar because we both copied the same source.

> 
> BTW: there had been similar issues reported for the Gumstix Overo:
> 
> http://wiki.gumstix.org/index.php?title=Overo_Wifi#Issues

Yes, same issue.

NeilBrown


> 
> BR,
> Nikolaus
> 

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