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[109.252.170.211]) by smtp.googlemail.com with ESMTPSA id 82sm2247569lfo.173.2020.09.25.06.21.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Sep 2020 06:21:19 -0700 (PDT) Subject: Re: [PATCH v2 1/4] dt-bindings: reserved-memory: Document "active" property To: Robin Murphy , Thierry Reding Cc: Joerg Roedel , Rob Herring , Frank Rowand , Will Deacon , iommu@lists.linux-foundation.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, "linux-tegra@vger.kernel.org" References: <20200904130000.691933-1-thierry.reding@gmail.com> <20200924140130.GA2527337@ulmo> <484b9e90-7395-6161-577c-4d3f3716997e@arm.com> From: Dmitry Osipenko Message-ID: <70712ca4-8971-3af4-d0d0-b73788d6cfa9@gmail.com> Date: Fri, 25 Sep 2020 16:21:17 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <484b9e90-7395-6161-577c-4d3f3716997e@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-tegra@vger.kernel.org 25.09.2020 15:39, Robin Murphy пишет: ... >> IIRC, in the past Robin Murphy was suggesting to read out hardware state >> early during kernel boot in order to find what regions are in use by >> hardware. > > I doubt I suggested that in general, because I've always firmly believed > it to be a terrible idea. I've debugged too many cases where firmware or > kexec has inadvertently left DMA running and corrupted kernel memory, so > in general we definitely *don't* want to blindly trust random hardware > state. Anything I may have said in relation to Qualcomm's fundamentally > broken hypervisor/bootloader setup should not be considered outside that > specific context ;) > > Robin. > >> I think it should be easy to do for the display controller since we >> could check clock and PD states in order to decide whether DC's IO could >> be accessed and then read out the FB pointer and size. I guess it should >> take about hundred lines of code. The active DMA is indeed very dangerous, but it's a bit less dangerous in a case of read-only DMA. I got another idea of how we could benefit from the active display hardware. Maybe we could do the following: 1. Check whether display is active 2. Allocate CMA that matches the FB size 3. Create identity mapping for the CMA 4. Switch display framebuffer to our CMA 5. Create very early simple-framebuffer out of the CMA 6. Once Tegra DRM driver is loaded, it will kick out the simple-fb, and thus, release temporal CMA and identity mapping. This will provide us with a very early framebuffer output and it will work on all devices out-of-the-box! 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[109.252.170.211]) by smtp.googlemail.com with ESMTPSA id 82sm2247569lfo.173.2020.09.25.06.21.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 25 Sep 2020 06:21:19 -0700 (PDT) Subject: Re: [PATCH v2 1/4] dt-bindings: reserved-memory: Document "active" property To: Robin Murphy , Thierry Reding References: <20200904130000.691933-1-thierry.reding@gmail.com> <20200924140130.GA2527337@ulmo> <484b9e90-7395-6161-577c-4d3f3716997e@arm.com> From: Dmitry Osipenko Message-ID: <70712ca4-8971-3af4-d0d0-b73788d6cfa9@gmail.com> Date: Fri, 25 Sep 2020 16:21:17 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <484b9e90-7395-6161-577c-4d3f3716997e@arm.com> Content-Language: en-US Cc: devicetree@vger.kernel.org, Frank Rowand , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Rob Herring , "linux-tegra@vger.kernel.org" , Will Deacon X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" MjUuMDkuMjAyMCAxNTozOSwgUm9iaW4gTXVycGh5INC/0LjRiNC10YI6Ci4uLgo+PiBJSVJDLCBp biB0aGUgcGFzdCBSb2JpbiBNdXJwaHkgd2FzIHN1Z2dlc3RpbmcgdG8gcmVhZCBvdXQgaGFyZHdh cmUgc3RhdGUKPj4gZWFybHkgZHVyaW5nIGtlcm5lbCBib290IGluIG9yZGVyIHRvIGZpbmQgd2hh dCByZWdpb25zIGFyZSBpbiB1c2UgYnkKPj4gaGFyZHdhcmUuCj4gCj4gSSBkb3VidCBJIHN1Z2dl c3RlZCB0aGF0IGluIGdlbmVyYWwsIGJlY2F1c2UgSSd2ZSBhbHdheXMgZmlybWx5IGJlbGlldmVk Cj4gaXQgdG8gYmUgYSB0ZXJyaWJsZSBpZGVhLiBJJ3ZlIGRlYnVnZ2VkIHRvbyBtYW55IGNhc2Vz IHdoZXJlIGZpcm13YXJlIG9yCj4ga2V4ZWMgaGFzIGluYWR2ZXJ0ZW50bHkgbGVmdCBETUEgcnVu bmluZyBhbmQgY29ycnVwdGVkIGtlcm5lbCBtZW1vcnksIHNvCj4gaW4gZ2VuZXJhbCB3ZSBkZWZp bml0ZWx5ICpkb24ndCogd2FudCB0byBibGluZGx5IHRydXN0IHJhbmRvbSBoYXJkd2FyZQo+IHN0 YXRlLiBBbnl0aGluZyBJIG1heSBoYXZlIHNhaWQgaW4gcmVsYXRpb24gdG8gUXVhbGNvbW0ncyBm dW5kYW1lbnRhbGx5Cj4gYnJva2VuIGh5cGVydmlzb3IvYm9vdGxvYWRlciBzZXR1cCBzaG91bGQg bm90IGJlIGNvbnNpZGVyZWQgb3V0c2lkZSB0aGF0Cj4gc3BlY2lmaWMgY29udGV4dCA7KQo+IAo+ IFJvYmluLgo+IAo+PiBJIHRoaW5rIGl0IHNob3VsZCBiZSBlYXN5IHRvIGRvIGZvciB0aGUgZGlz cGxheSBjb250cm9sbGVyIHNpbmNlIHdlCj4+IGNvdWxkIGNoZWNrIGNsb2NrIGFuZCBQRCBzdGF0 ZXMgaW4gb3JkZXIgdG8gZGVjaWRlIHdoZXRoZXIgREMncyBJTyBjb3VsZAo+PiBiZSBhY2Nlc3Nl ZCBhbmQgdGhlbiByZWFkIG91dCB0aGUgRkIgcG9pbnRlciBhbmQgc2l6ZS4gSSBndWVzcyBpdCBz aG91bGQKPj4gdGFrZSBhYm91dCBodW5kcmVkIGxpbmVzIG9mIGNvZGUuCgpUaGUgYWN0aXZlIERN QSBpcyBpbmRlZWQgdmVyeSBkYW5nZXJvdXMsIGJ1dCBpdCdzIGEgYml0IGxlc3MgZGFuZ2Vyb3Vz CmluIGEgY2FzZSBvZiByZWFkLW9ubHkgRE1BLgoKSSBnb3QgYW5vdGhlciBpZGVhIG9mIGhvdyB3 ZSBjb3VsZCBiZW5lZml0IGZyb20gdGhlIGFjdGl2ZSBkaXNwbGF5CmhhcmR3YXJlLiBNYXliZSB3 ZSBjb3VsZCBkbyB0aGUgZm9sbG93aW5nOgoKMS4gQ2hlY2sgd2hldGhlciBkaXNwbGF5IGlzIGFj dGl2ZQoKMi4gQWxsb2NhdGUgQ01BIHRoYXQgbWF0Y2hlcyB0aGUgRkIgc2l6ZQoKMy4gQ3JlYXRl IGlkZW50aXR5IG1hcHBpbmcgZm9yIHRoZSBDTUEKCjQuIFN3aXRjaCBkaXNwbGF5IGZyYW1lYnVm ZmVyIHRvIG91ciBDTUEKCjUuIENyZWF0ZSB2ZXJ5IGVhcmx5IHNpbXBsZS1mcmFtZWJ1ZmZlciBv dXQgb2YgdGhlIENNQQoKNi4gT25jZSBUZWdyYSBEUk0gZHJpdmVyIGlzIGxvYWRlZCwgaXQgd2ls bCBraWNrIG91dCB0aGUgc2ltcGxlLWZiLCBhbmQKdGh1cywgcmVsZWFzZSB0ZW1wb3JhbCBDTUEg YW5kIGlkZW50aXR5IG1hcHBpbmcuCgpUaGlzIHdpbGwgcHJvdmlkZSB1cyB3aXRoIGEgdmVyeSBl YXJseSBmcmFtZWJ1ZmZlciBvdXRwdXQgYW5kIGl0IHdpbGwKd29yayBvbiBhbGwgZGV2aWNlcyBv dXQtb2YtdGhlLWJveCEKX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX18KaW9tbXUgbWFpbGluZyBsaXN0CmlvbW11QGxpc3RzLmxpbnV4LWZvdW5kYXRpb24ub3Jn Cmh0dHBzOi8vbGlzdHMubGludXhmb3VuZGF0aW9uLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2lvbW11