linux-kernel - Re: [PATCH v1 12/12] serial: 8250_lpss: enable DMA on Intel Quark UART

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Date:	Tue, 12 Apr 2016 19:50:24 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Bryan O'Donoghue <pure.logic@...us-software.ie>,
	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	dmaengine <dmaengine@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Puustinen, Ismo" <ismo.puustinen@...el.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: Re: [PATCH v1 12/12] serial: 8250_lpss: enable DMA on Intel Quark
 UART

On Tue, 2016-04-12 at 17:25 +0100, Bryan O'Donoghue wrote:
> On Mon, 2016-04-11 at 18:51 +0300, Andy Shevchenko wrote:
> > 
> > On Mon, Apr 11, 2016 at 6:33 PM, Bryan O'Donoghue
> > <pure.logic@...us-software.ie> wrote:
> > > 
> > > On Thu, 2016-04-07 at 23:37 +0300, Andy Shevchenko wrote:
> > > 
> > > Preface. I tried this on Galileo and it appears to work. I'll do
> > > some
> > > throughput testing to verify but, initially the results are
> > > positive :)
> > I submitted (and pushed into my branch) a bit changed version (see
> > my
> > v2).
> > 
> > > 
> > > > 
> > > > +       lpss->dma_maxburst = 8;
> > > Are these dwords ? If those are bytes then the maxburst value
> > > looks
> > > small. In the BSP the max burst is 32 bytes.
> > max_burst is in items of given size (here is 32 bytes for memory
> > and 
> > 8
> I haven't read your V2 yet but on this, I'd suggest raising the burst
> size to 32 bytes for UART (no higher) we found during bringup that
> larger sizes "fall-over and die" but, anything up to 32 bytes is OK -
> and therefore you should be able to reduce the number of
> bursts/interrupts etc.

It can't be more that FIFO size and recommendation as far as I know is
FIFO/2, which is exactly 8 bytes.

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy