From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Warren Subject: Re: [PATCH 1/5] ARM: DT: tegra114: add APB DMA controller DT entry Date: Fri, 08 Mar 2013 11:41:23 -0700 Message-ID: <513A30D3.4020700@wwwdotorg.org> References: <1362750782-15174-1-git-send-email-ldewangan@nvidia.com> <1362750782-15174-2-git-send-email-ldewangan@nvidia.com> <513A250C.1000202@wwwdotorg.org> <513A2888.5020402@nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <513A2888.5020402-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Laxman Dewangan Cc: "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Peter De Schrijver List-Id: linux-tegra@vger.kernel.org On 03/08/2013 11:06 AM, Laxman Dewangan wrote: > On Friday 08 March 2013 11:21 PM, Stephen Warren wrote: >> On 03/08/2013 06:52 AM, Laxman Dewangan wrote: >>> NVIDIA's Tegra114 has 32 channels APB DMA controller. Add DT entry for >>> APB DMA controllers and make it compatible with >>> "nvidia,tegra114-apbdma". >>> diff --git a/arch/arm/boot/dts/tegra114.dtsi >>> b/arch/arm/boot/dts/tegra114.dtsi >>> + apbdma: dma { >>> + compatible = "nvidia,tegra114-apbdma"; >> So I know that the Tegra114 HW has a new channel-pause feature, which >> the driver /can/ use. However, if the driver didn't know about that >> feature, and continued to use the global-pause feature, would it still >> work fine? >> >> In other words, is the Tegra114 HW 100% backwards-compatible with the >> Tegra30 HW, it's just that there are new features that SW could >> optionally use? >> >> If that is true, then we should also include "nvidia,tegra30-apbdma" in >> the compatible value. > > Tegra114 HW is not compatible with the tegra30 as with global pause, it > is not able to write into the dma register in T114. On t114, the dma > register is clock gated with global enable/disable. Interesting. In that case, the compatible value above is entirely correct. Thanks for the explanation. It might be worth mentioning this in the commit description.