Messages in this thread | | | From | "Guzman Lugo, Fernando" <> | Date | Thu, 26 Aug 2010 08:16:24 -0500 | Subject | RE: [PATCH 8/9] dspbridge: add map support for big buffers |
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>________________________________________ >From: FUJITA Tomonori [fujita.tomonori@lab.ntt.co.jp] >Sent: Thursday, August 26, 2010 7:56 AM >To: Guzman Lugo, Fernando >Cc: fujita.tomonori@lab.ntt.co.jp; linux-omap@vger.kernel.org; linux-kernel@vger.kernel.org; ohad@wizery.com; hiroshi.doyu@nokia.com; ameya.palande@nokia.com; >felipe.contreras@nokia.com >Subject: RE: [PATCH 8/9] dspbridge: add map support for big buffers > >On Thu, 26 Aug 2010 07:38:26 -0500 >"Guzman Lugo, Fernando" <fernando.lugo@ti.com> wrote: > >> >> due to a restriction in scatter gather lists, it can >> >> not be created a list for a buffer bigger than 1MB. >> >> This patch is spliting big mappings into 1MB mappings. >> > >> >I don't read the whole thread but the above description is incorrect. >> > >> >Why can't you use scatter gather chaining? You can create a scatter >> >list for a buffer larger than 1MB. >> >> The thing is that ARM architecture does not support SG chaining. This patch should be >> seen like a workaround until it is fixed in iovmm module. > >Fix iovmm module is easier than the workaround?
I have not thought about possible fixes inside iovmm, but now I am reviewing the patches I will figure out how to fix this inside iovmm. Since he workaround still can fail to allocate big buffers even though there is space to allocate it.
> >From a quick look, arch/arm/plat-omap/iovmm.c does nothing wrong about >scatter gather chaining. arm/arm/mm/dma-mapping.c looks fine too about >it. Maybe just defining ARCH_HAS_SG_CHAIN works?
I can try, but it looks tricky for me. Maybe someone else can tell us why SG chain is not supported for ARM or if there is a problem just defining ARCH_HAS_SG_CHAIN.
Regards, Fernando.
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