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

[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.

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.

NeilBrown

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