From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tomasz Figa <t.figa-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
Subject: Re: [PATCH v11 20/27] iommu/exynos: allow having multiple System MMUs
	for a master H/W
Date: Fri, 14 Mar 2014 17:12:03 +0100
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References: <20140314141050.c8bedcb66532d277c496796d@samsung.com>
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To: Cho KyongHo <pullip.cho-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>, Linux ARM Kernel <linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>, Linux DeviceTree <devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux IOMMU <iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>, Linux Kernel <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux Samsung SOC <linux-samsung-soc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Cc: Kukjin Kim <kgene.kim-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>, Prathyush <prathyush.k-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>, Grant Grundler <grundler-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>, Sachin Kamat <sachin.kamat-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>, Sylwester Nawrocki <s.nawrocki-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>, Varun Sethi <Varun.Sethi-KZfg59tc24xl57MIdRCFDg@public.gmane.org>, Antonios Motakis <a.motakis-lrHrjnjw1UfHK3s98zE1ajGjJy/sRE9J@public.gmane.org>, Rahul Sharma <rahul.sharma-Sze3O3UU22JBDgjK7y7TUQ@public.gmane.org>
List-Id: iommu@lists.linux-foundation.org

Hi KyongHo,

On 14.03.2014 06:10, Cho KyongHo wrote:
> Some master device descriptor like fimc-is which is an abstraction
> of very complex H/W may have multiple System MMUs. For those devices,
> the design of the link between System MMU and its master H/W is needed
> to be reconsidered.
>
> A link structure, sysmmu_list_data is introduced that provides a link
> to master H/W and that has a pointer to the device descriptor of a
> System MMU. Given a device descriptor of a master H/W, it is possible
> to traverse all System MMUs that must be controlled along with the
> master H/W.

NAK.

A device driver should handle particular hardware instances separately, 
without abstracting a virtual hardware instance consisting of multiple 
physical ones.

If such abstraction is needed, it should be done above the exynos-iommu 
driver, e.g. by something like iommu-composite driver that would 
aggregate several IOMMUs. Keep in mind that such IOMMUs in a group could 
be different, e.g. different Exynos SysMMU versions or even completely 
different IPs handled by different drivers.

Still, I don't think there is a real need for such abstraction. Instead, 
related drivers shall be fixed to properly handle multiple memory 
masters and their IOMMUs.

Best regards,
Tomasz