linux-kernel - Re: [PATCHv4 0/8] Support for Tegra 2D hardware

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Date:	Thu, 03 Jan 2013 13:55:43 +0800
From:	Mark Zhang <nvmarkzhang@...il.com>
To:	Terje Bergström <tbergstrom@...dia.com>
CC:	"thierry.reding@...onic-design.de" <thierry.reding@...onic-design.de>,
	"airlied@...ux.ie" <airlied@...ux.ie>,
	"dev@...xeye.de" <dev@...xeye.de>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv4 0/8] Support for Tegra 2D hardware

On 01/03/2013 01:50 PM, Terje Bergström wrote:
> On 03.01.2013 05:31, Mark Zhang wrote:
>> Sorry I didn't get it. Yes, in current design, you can pin all mem
>> handles in one time but I haven't found anything related with "locking
>> only once per submit".
>>
>> My idea is:
>> - remove "job->addr_phys"
>> - assign "job->reloc_addr_phys" & "job->gather_addr_phys" separately
>> - In "pin_job_mem", just call "host1x_memmgr_pin_array_ids" twice to
>> fill the "reloc_addr_phy" & "gather_addr_phys".
>>
>> Anything I misunderstood?
> 
> The current design uses CMA, which makes pinning basically a no-op. When
> we have IOMMU support, pinning requires calling into IOMMU. Updating
> SMMU tables requires locking, and probably maintenance before SMMU code
> also requires its own locked data tables. For example, preventing
> duplicate pinning might require a global table of handles.
> 
> Putting all of the handles in one table allows doing duplicate detection
> across cmdbuf and reloc tables. This allows pinning each buffer exactly
> once, which reduces number of calls to IOMMU.
> 

Thanks Terje. Yes, I understand IOMMU will bring in more operations. But
I'm not convinced that separating 2 arrays have lots of overheads than
putting them into one array.

But it doesn't matter, after the IOMMU support version released, I can
read this part of codes again. Let's talk about this at that time.

>> "host1x_cma_pin_array_ids" doesn't return negative value right now, so
>> maybe you need to take a look at it.
> 
> True, and also a consequence of using CMA: pinning can never fail. With
> IOMMU, pinning can fail.

Got it. Agree.

> 
> Terje
> 
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