From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Kocialkowski Subject: Re: [PATCH v2 09/10] ARM: dts: sun7i-a20: Add Video Engine and reserved memory nodes Date: Fri, 04 May 2018 10:47:44 +0200 Message-ID: References: <20180419154124.17512-1-paul.kocialkowski@bootlin.com> <20180419154536.17846-5-paul.kocialkowski@bootlin.com> <20180420073908.nkcbsdxibnzkqski@flea> <82057e2f734137a3902d9313c228b01ceb345ee7.camel@bootlin.com> <20180504084008.h6p4brari3xrbv6l@flea> Reply-To: paul.kocialkowski-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org Mime-Version: 1.0 Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-z6uOXkhlZI6BuzvAQsoF" Return-path: Sender: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org In-Reply-To: <20180504084008.h6p4brari3xrbv6l@flea> List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , To: Maxime Ripard Cc: linux-media-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org, Mauro Carvalho Chehab , Rob Herring , Mark Rutland , Chen-Yu Tsai , Pawel Osciak , Marek Szyprowski , Kyungmin Park , Hans Verkuil , Sakari Ailus , Philipp Zabel , Arnd Bergmann , Alexandre Courbot , Tomasz Figa List-Id: devicetree@vger.kernel.org --=-z6uOXkhlZI6BuzvAQsoF Content-Type: text/plain; charset="UTF-8" Hi, On Fri, 2018-05-04 at 10:40 +0200, Maxime Ripard wrote: > On Fri, May 04, 2018 at 09:49:16AM +0200, Paul Kocialkowski wrote: > > > > + reserved-memory { > > > > + #address-cells = <1>; > > > > + #size-cells = <1>; > > > > + ranges; > > > > + > > > > + /* Address must be kept in the lower 256 MiBs > > > > of > > > > DRAM for VE. */ > > > > + ve_memory: cma@4a000000 { > > > > + compatible = "shared-dma-pool"; > > > > + reg = <0x4a000000 0x6000000>; > > > > + no-map; > > > > > > I'm not sure why no-map is needed. > > > > In fact, having no-map here would lead to reserving the area as > > cache- > > coherent instead of contiguous and thus prevented dmabuf support. > > Replacing it by "resuable" allows proper CMA reservation. > > > > > And I guess we could use alloc-ranges to make sure the region is > > > in > > > the proper memory range, instead of hardcoding it. > > > > As far as I could understand from the documentation, "alloc-ranges" > > is > > used for dynamic allocation while only "reg" is used for static > > allocation. We are currently going with static allocation and thus > > reserve the whole 96 MiB. Is using dynamic allocation instead > > desirable > > here? > > I guess we could turn the question backward. Why do we need a static > allocation? This isn't a buffer that is always allocated on the same > area, but rather that we have a range available. So our constraint is > on the range, nothing else. That makes sense, I will give it a shot with a range then. > > > > + reg = <0x01c0e000 0x1000>; > > > > + memory-region = <&ve_memory>; > > > > > > Since you made the CMA region the default one, you don't need to > > > tie > > > it to that device in particular (and you can drop it being > > > mandatory > > > from your binding as well). > > > > What if another driver (or the system) claims memory from that zone > > and > > that the reserved memory ends up not being available for the VPU > > anymore? > > > > Acccording to the reserved-memory documentation, the reusable > > property > > (that we need for dmabuf) puts a limitation that the device driver > > owning the region must be able to reclaim it back. > > > > How does that work out if the CMA region is not tied to a driver in > > particular? > > I'm not sure to get what you're saying. You have the property > linux,cma-default in your reserved region, so the behaviour you > described is what you explicitly asked for. My point is that I don't see how the driver can claim back (part of) the reserved area if the area is not explicitly attached to it. Or is that mechanism made in a way that all drivers wishing to use the reserved memory area can claim it back from the system, but there is no priority (other than first-come first-served) for which drivers claims it back in case two want to use the same reserved region (in a scenario where there isn't enough memory to allow both drivers)? > > > > + > > > > + clocks = <&ccu CLK_AHB_VE>, <&ccu > > > > CLK_VE>, > > > > + <&ccu CLK_DRAM_VE>; > > > > + clock-names = "ahb", "mod", "ram"; > > > > + > > > > + assigned-clocks = <&ccu CLK_VE>; > > > > + assigned-clock-rates = <320000000>; > > > > > > This should be set from within the driver. If it's something that > > > you > > > absolutely needed for the device to operate, you have no guarantee > > > that the clock rate won't change at any point in time after the > > > device > > > probe, so that's not a proper solution. > > > > > > And if it's not needed and can be adjusted depending on the > > > framerate/codec/resolution, then it shouldn't be in the DT either. > > > > Yes, that makes sense. > > > > > Don't you also need to map the SRAM on the A20? > > > > That's a good point, there is currently no syscon handle for A20 > > (and > > also A13). Maybe SRAM is muxed to the VE by default so it "just > > works"? > > > > I'll investigate on this side, also keeping in mind that the actual > > solution is to use the SRAM controller driver (but that won't make > > it to > > v3). > > The SRAM driver is available on the A20, so you should really use that > instead of a syscon. The SRAM driver is indeed available for the A20, but still lacks support for the VE in particular as far as I can see. Cheers, -- Paul Kocialkowski, Bootlin (formerly Free Electrons) Embedded Linux and kernel engineering https://bootlin.com --=-z6uOXkhlZI6BuzvAQsoF--