From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mitchel Humpherys Subject: Re: [PATCH v2] of: Check for overlap in reserved memory regions Date: Fri, 04 Dec 2015 09:27:50 -0800 Message-ID: References: <1442367036-15205-1-git-send-email-mitchelh@codeaurora.org> <1447294799.29472.15.camel@ellerman.id.au> Mime-Version: 1.0 Content-Type: text/plain Return-path: In-Reply-To: <1447294799.29472.15.camel@ellerman.id.au> (Michael Ellerman's message of "Thu, 12 Nov 2015 13:19:59 +1100") Sender: linux-kernel-owner@vger.kernel.org To: Michael Ellerman Cc: Rob Herring , Frank Rowand , Grant Likely , devicetree@vger.kernel.org, Marek Szyprowski , linux-kernel@vger.kernel.org List-Id: devicetree@vger.kernel.org On Thu, Nov 12 2015 at 01:19:59 PM, Michael Ellerman wrote: > On Tue, 2015-09-15 at 18:30 -0700, Mitchel Humpherys wrote: > >> Any overlap in the reserved memory regions (those specified in the >> reserved-memory DT node) is a bug. > > Can you expand a bit on why you think it's a bug? I assume it was discussed at > some point on the list but I didn't see it sorry. The reason I think it's a bug is because the overlapping memory could be handed out to multiple firmwares, which generally ends in "random" firmware crashes. We've found by sad experience that root-causing such a crash can be quite difficult. Is there a valid use case for overlapping regions? I can't think of one... > There's nothing I can see in the binding document[1] about whether regions can > overlap, or what it would mean if they did. You're right, the bindings document doesn't say anything about overlapping memory regions. I can submit something unless someone comes up with a reason why we should allow overlapping memory regions. > If we want to declare that overlapping regions are always a bug then there > should be some text in the binding explaining that. There's also the > possibility that we have existing device trees in the wild that contain > overlapping regions, and whether we think it's OK to retrospectively declare > that they're incorrect. I did a quick survey of in-tree users of reserved-memory and couldn't find any overlapping regions. -Mitch -- Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project