linux-kernel - Re: dmatest no longer works on ARC SDP with DW DMAC

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Date:	Wed, 10 Aug 2016 12:22:41 +0000
From:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>
To:	"andriy.shevchenko@...ux.intel.com" 
	<andriy.shevchenko@...ux.intel.com>
CC:	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>,
	"Eugeniy.Paltsev@...opsys.com" <Eugeniy.Paltsev@...opsys.com>,
	"Nelson.Pereira@...opsys.com" <Nelson.Pereira@...opsys.com>,
	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>,
	"viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>
Subject: Re: dmatest no longer works on ARC SDP with DW DMAC

Hi Andy,

On Wed, 2016-08-10 at 15:15 +0300, Andy Shevchenko wrote:
> On Wed, 2016-08-10 at 11:06 +0000, Eugeniy Paltsev wrote:
> > 
> > dmatest on ARC SDP with DW DMAC became broken after df5c7386
> > ("dmaengine: dw: some Intel devices has no memcpy support") and
> > 30cb2639 ("dmaengine: dw: don't override platform data with autocfg")
> > commits.
> > * After df5c7386 commit "DMA_MEMCPY" capability option doesn't
> > get set correctly in platform driver version.
> > * After 30cb2639 commit
> > "data_width" and "nollp" parameters don't get set correctly in
> > platform
> > driver version.
> > 
> > This happens because in old driver version there are three sources 
> > of parameters: pdata, device tree and autoconfig hardware registers. 
> > Some parameters were read from pdata and others from autoconfig
> > hardware registers. If pdata was absent some pdata structure 
> > fields were filled with parameters from device tree. But 30cb2639
> > commit disabled overriding pdata with autocfg, so if we use platform
> > driver version without pdata some parameters will not be set.
> 
> Yes, that's correct behaviour right now. You have to provide platform
> code which registers device with all platform data provided.

But given autocfg registers exist in HW why don't we rely on their contents?

> > I'm wondering what would be the best way to fix this situation?
> 
> Ideally we have to switch to use built-in device properties
> (drivers/base/property.c) and platform code in your case has to provide
> properties.

What do you mean saying "built-in device properties"?
Setting pdata structure? In our particular case we use device tree
for DW DMAC setup.

-Alexey