[Patch v4] OMAP: sDMA driver: descriptor autoloading feature

[Shilimkar, Santosh]

________________________________________
From: adrian.hunter at nokia.com [mailto:adrian.hunter at nokia.com] 
Sent: Thursday, January 07, 2010 1:30 PM
To: S, Venkatraman
Cc: tony at atomide.com; linux at arm.linux.org.uk; Shilimkar, Santosh; khilman at deeprootsystems.com; linux-omap at vger.kernel.org; linux-arm-kernel at lists.infradead.org; jarkko.lavinen at nokia.com
Subject: Re: [Patch v4] OMAP: sDMA driver: descriptor autoloading feature

Venkatraman S wrote: 
> On Wed, Jan 6, 2010 at 6:46 PM, Adrian Hunter <adrian.hunter at nokia.com> 
> wrote: 
> > Venkatraman S wrote: 
> > > 
> > > On Tue, Dec 29, 2009 at 3:18 AM, Tony Lindgren <tony at atomide.com> 
> wrote: 
> > > > 
> > > > * Venkatraman S <svenkatr at ti.com> [091211 07:01]: 
> > > > > 
> > > > > Here is the most updated version of the patch (thanks to Russell's 
> > > > > review). This patch is applicable to OMAP4xxx as well as OMAP3630 
> > > > > Reference to previous posts 
> > > > > v1  http://marc.info/?l=linux-omap&m=125012097403050&w=2 
> > > > > v2  http://marc.info/?l=linux-omap&m=125137152606644&w=2 
> > > > > v3  http://patchwork.kernel.org/patch/45408/ 
> > > > 
> > > > Do you have a patch for drivers/mmc/host/omap_hsmmc.c to 
> > > > use this feature? Or some other driver? 
> > > > 
> > > > Regards, 
> > > > 
> > > > Tony 
> > > 
> > > I am about to start working on omap_hsmmc to use the descriptor load 
> > > feature. If the DMA changes are acceptable, I can post the driver 
> > > patch as well. 
> > 
> > I presume this is about performance.  How does it compare to chained 
> DMA? 
> > We have a patch for omap_hsmmc for chained DMA that we are still 
> testing. 
> > 
>  The main difference would be the number of logical channels used. 
> With chaining, I assume you'd request for (or the API internally 
> reserves) as many logical channels as there are segments. Here a 
> single logical channel would do. 
> 

How does the performance compare? Which is faster? Does descriptor autoloading reduce the number of interrupts? 
>>
This should improve the perforamance compared to chaining  case. This features emulates
scatter gather transfers capability with minimum MPU support by removing the
successive channel configuration processing and the associated interrupt handling overheads. 
This is apart from optimize channel resources by enabling efficient transfer “serialization” on a single logical channel versus concurrent (multiple) logical channel usage. 

Regards,
Santosh