linux-kernel - Re: Wrong "nollp" DW DMAC parameter value on ARC SDP.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <1471010908.4887.100.camel@linux.intel.com>
Date:	Fri, 12 Aug 2016 17:08:28 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>
Cc:	"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
	"Nelson.Pereira@...opsys.com" <Nelson.Pereira@...opsys.com>,
	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"linux-snps-arc@...ts.infradead.org" 
	<linux-snps-arc@...ts.infradead.org>
Subject: Re: Wrong "nollp" DW DMAC parameter value on ARC SDP.

On Fri, 2016-08-12 at 13:36 +0000, Eugeniy Paltsev wrote:
> On Fri, 2016-08-12 at 13:59 +0300, Andy Shevchenko wrote:
> > 
> > On Fri, 2016-08-12 at 08:03 +0000, Eugeniy Paltsev wrote:
> > > 
> > > 
> > > Hi,
> > > 
> > > "nollp" parameter defines if DW DMAC channel supports multi block
> > > transfer or not.
> > > 
> > > It is calculated in runtime, but differently depending on on
> > > availability of pdata. If pdata is absent "nollp" is calculated
> > > using
> > > autoconfig hardware registers. Otherwise "nollp" is calculated
> > > using
> > > the next code construction:
> > > channel_writel(dwc, LLP, DWC_LLP_LOC(0xffffffff));
> > > dwc->nollp = DWC_LLP_LOC(channel_readl(dwc, LLP)) == 0;
> > > channel_writel(dwc, LLP, 0);
> > > 
> > > I realized that these methods give different results.
> > > For example on ARC AXS101 SDP in case of using autoconfig "nollp"
> > > was
> > > calculated as "true" (and DMAC works fine), 
> > > otherwise "nollp" was calculated as "false" (and DMAC doesn't
> > > work).
> > Can you show out what the value you read back?
> 
> channel_readl(dwc, LLP) return 0xfffffffc

Nice.

Oh, forgot to ask, what are the DW_PARAMS and DWC_PARAMS[x] are on the
same hardware?

I assume we are talking about that one which has no hardware LLP
support.

> > > So I'm wondering how the code in question really works?
> > > From DW AHB DMAC databook I wasn't able to find anything relevant
> > > to
> > > this tricky implementation. Could you please clarify a little but
> > > what
> > > happens here?
> > "Table 4-1:
> > ...
> > Hardcode Channel x LLP register to 0?
> > ...
> > Description: If set to 1, hardcodes channel x Linked List Pointer
> > register to 0 (LLPx.LOC == 0), ..."

So, any comment on this one? I suppose you may have an access to some
internal Synopsys documentation which might shed a light. Or maybe I
missed something else which should be considered.

> > > Maybe we should add "nollp" field in pdata structure and receive
> > > it
> > > from pdata/device tree (like we use "is_private" or "is_memcpu"
> > > fields)
> > Yeah, perhaps we can remove that trick since we need this flag to be
> > set
> > on Intel Quark which might have the same issue as your case [1].
> > 
> > [1] http://www.spinics.net/lists/linux-serial/msg22948.html
> > 
> 
> In which tree I can find this patch applied, so I may base my work on
> it?

The series is under review. I'm preparing v10, so, I would like to re-
make this patch with regarding to your input.

For now I would prefer just to remove the trick, but I still wonder what
the circumstances are to bring it not working.

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