linux-kernel - Re: [PATCH 16/18] dmaengine/amba-pl08x: Add support for sg len greater than one for slave transfers

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: <4E4CCF7B.8060704@st.com>
Date:	Thu, 18 Aug 2011 14:08:19 +0530
From:	Viresh Kumar <viresh.kumar@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	"linus.walleij@...aro.org" <linus.walleij@...aro.org>
Cc:	Pratyush ANAND <pratyush.anand@...com>,
	Rajeev KUMAR <rajeev-dlh.kumar@...com>,
	Bhupesh SHARMA <bhupesh.sharma@...com>,
	Shiraz HASHIM <shiraz.hashim@...com>,
	"vinod.koul@...el.com" <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vipin KUMAR <vipin.kumar@...com>,
	Armando VISCONTI <armando.visconti@...com>,
	Amit VIRDI <Amit.VIRDI@...com>,
	Vipul Kumar SAMAR <vipulkumar.samar@...com>,
	"viresh.linux@...il.com" <viresh.linux@...il.com>,
	Deepak SIKRI <deepak.sikri@...com>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 16/18] dmaengine/amba-pl08x: Add support for sg len greater
 than one for slave transfers


Hi Russell & Linus,

Sorry for being late to reply.

On 8/14/2011 2:06 PM, Russell King - ARM Linux wrote:
> On Fri, Jul 29, 2011 at 04:19:26PM +0530, Viresh Kumar wrote:
>> Untill now, sg_len greater than one is not supported. This patch adds support to
>> do that.
> 
> I'm not sure that this is the correct approach.  memcpy()s can only be
> used with one single buffer, so the sg stuff for that (and the unmapping
> support) doesn't make sense at all.
> 

I am not sure if i get this completely. In memcpy, we still don't support
more than one sg. We have created a new member in txd, which keeps track of
data (addresses, len).

While unmapping, we are unmapping only single dsg. I think i don't need to
use list_for_each_entry() there, as there is only one element present in list.
But can still keep that.

> The only place where this makes sense is the slave sg stuff.  I wonder
> whether we can better deal with that by having the LLI setup code deal
> with one SG list entry at a time, and chain each together.
> 
> Something I've also been pondering which is related to this is linking
> together DMA operations using the LLI chaining when interrupts and
> callbacks aren't required.  It's a very similar problem.  Other DMA
> engine drivers do this.
> 

Are you talking about linking all sg's together or linking multiple calls to
prep_dma_memcpy? I am handling the first.

> Finally, note that some of the PL08x code assumes that for any TXD,
> the LLI list is a contiguous array.  See the first part of
> pl08x_getbytes_chan(). That needs fixing as soon as we start going to
> more than one SG list entry.

We still have one contiguous array for LLI list. In pl08x_fill_llis_for_desc()
i am using same txd->llis_va for all sg's.

Sorry if i misunderstood your concerns.

-- 
viresh
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/