linux-kernel - RE: [PATCH 8/9] dspbridge: add map support for big buffers

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Date:	Fri, 2 Jul 2010 11:27:09 -0500
From:	"Guzman Lugo, Fernando" <fernando.lugo@...com>
To:	"Kanigeri, Hari" <h-kanigeri2@...com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"ohad@...ery.com" <ohad@...ery.com>,
	"hiroshi.doyu@...ia.com" <hiroshi.doyu@...ia.com>,
	"ameya.palande@...ia.com" <ameya.palande@...ia.com>,
	"felipe.contreras@...ia.com" <felipe.contreras@...ia.com>
Subject: RE: [PATCH 8/9] dspbridge: add map support for big buffers



Hi Hari,

> -----Original Message-----
> From: Kanigeri, Hari
> Sent: Thursday, July 01, 2010 6:36 PM
> To: Guzman Lugo, Fernando; linux-omap@...r.kernel.org; linux-
> kernel@...r.kernel.org
> Cc: ohad@...ery.com; hiroshi.doyu@...ia.com; ameya.palande@...ia.com;
> felipe.contreras@...ia.com; Guzman Lugo, Fernando
> Subject: RE: [PATCH 8/9] dspbridge: add map support for big buffers
> 
> Fernando,
> 
> > -	for_each_sg(sgt->sgl, sg, sgt->nents, i)
> > -		sg_set_page(sg, usr_pgs[i], PAGE_SIZE, 0);
> > +		da = iommu_vmap(mmu, da, sgt, IOVMF_ENDIAN_LITTLE |
> > +							IOVMF_ELSZ_32);
> 
> -- iommu_vmap does the Kernel mapping to the buffers you are mapping to
> DSP MMU. Why do you need Kernel mappings ?
> 
> If there is no benefit in maintaining Kernel mapping I would rather call
> iopgtable_store_entry directly to map the entries.

Where inside iommu_vmap is the mapping done? I thought the kernel can access to that buffer after get_user_pages() where the user pages are pin and we can get a kernel address. The intention using iommu_vmap was to use api's proved by the iovmmu module. iommu_vmap() it is also tracking the mapped areas, so maybe the next step could be: remove dmm.c/h files and also proc_reserve/unreserved functions. If you think the function is unneeded steps and could affect the performance I can do the change to use only iopgtable_store_entry().

I think a kernel mapping is needed for flush/invalidate api's, please correct me if I am wrong. 

Regards,
Fernando.

> 
> Thank you,
> Best regards, Hari
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