Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v8 1/6] drm/fourcc: Add modifier definitions for
 describing Amlogic Video Framebuffer Compression
To:     Daniel Vetter <daniel@ffwll.ch>
Cc:     Simon Ser <contact@emersion.fr>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "jianxin.pan@amlogic.com" <jianxin.pan@amlogic.com>,
        Kevin Hilman <khilman@baylibre.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-amlogic@lists.infradead.org" 
        <linux-amlogic@lists.infradead.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
References: <20200702074759.32356-1-narmstrong@baylibre.com>
 <20200702074759.32356-2-narmstrong@baylibre.com>
 <8cBfZpkc4pHBLhihlvJMD_Hq1DEsNRcSY4Y8JaGwklMWcxiYzUMVEx7wH9f_DuCBMVUhXvOR0PcHVslILtKI2wdw79Nfih0N3VnrxfMQd08=@emersion.fr>
 <20200702131834.GZ3278063@phenom.ffwll.local>
 <044964ad-b927-57d7-9361-beda5c8d99a8@baylibre.com>
 <CAKMK7uHa4ajC5_SA_fFUhB-Amxcbt7T9UZ+pvRhqDeUeX9Ez6A@mail.gmail.com>
From:   Neil Armstrong <narmstrong@baylibre.com>
Autocrypt: addr=narmstrong@baylibre.com; prefer-encrypt=mutual; keydata=
 xsBNBE1ZBs8BCAD78xVLsXPwV/2qQx2FaO/7mhWL0Qodw8UcQJnkrWmgTFRobtTWxuRx8WWP
 GTjuhvbleoQ5Cxjr+v+1ARGCH46MxFP5DwauzPekwJUD5QKZlaw/bURTLmS2id5wWi3lqVH4
 BVF2WzvGyyeV1o4RTCYDnZ9VLLylJ9bneEaIs/7cjCEbipGGFlfIML3sfqnIvMAxIMZrvcl9
 qPV2k+KQ7q+aXavU5W+yLNn7QtXUB530Zlk/d2ETgzQ5FLYYnUDAaRl+8JUTjc0CNOTpCeik
 80TZcE6f8M76Xa6yU8VcNko94Ck7iB4vj70q76P/J7kt98hklrr85/3NU3oti3nrIHmHABEB
 AAHNKE5laWwgQXJtc3Ryb25nIDxuYXJtc3Ryb25nQGJheWxpYnJlLmNvbT7CwHsEEwEKACUC
 GyMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheABQJXDO2CAhkBAAoJEBaat7Gkz/iubGIH/iyk
 RqvgB62oKOFlgOTYCMkYpm2aAOZZLf6VKHKc7DoVwuUkjHfIRXdslbrxi4pk5VKU6ZP9AKsN
 NtMZntB8WrBTtkAZfZbTF7850uwd3eU5cN/7N1Q6g0JQihE7w4GlIkEpQ8vwSg5W7hkx3yQ6
 2YzrUZh/b7QThXbNZ7xOeSEms014QXazx8+txR7jrGF3dYxBsCkotO/8DNtZ1R+aUvRfpKg5
 ZgABTC0LmAQnuUUf2PHcKFAHZo5KrdO+tyfL+LgTUXIXkK+tenkLsAJ0cagz1EZ5gntuheLD
 YJuzS4zN+1Asmb9kVKxhjSQOcIh6g2tw7vaYJgL/OzJtZi6JlIXOwU0EVid/pAEQAND7AFhr
 5faf/EhDP9FSgYd/zgmb7JOpFPje3uw7jz9wFb28Cf0Y3CcncdElYoBNbRlesKvjQRL8mozV
 9RN+IUMHdUx1akR/A4BPXNdL7StfzKWOCxZHVS+rIQ/fE3Qz/jRmT6t2ZkpplLxVBpdu95qJ
 YwSZjuwFXdC+A7MHtQXYi3UfCgKiflj4+/ITcKC6EF32KrmIRqamQwiRsDcUUKlAUjkCLcHL
 CQvNsDdm2cxdHxC32AVm3Je8VCsH7/qEPMQ+cEZk47HOR3+Ihfn1LEG5LfwsyWE8/JxsU2a1
 q44LQM2lcK/0AKAL20XDd7ERH/FCBKkNVzi+svYJpyvCZCnWT0TRb72mT+XxLWNwfHTeGALE
 +1As4jIS72IglvbtONxc2OIid3tR5rX3k2V0iud0P7Hnz/JTdfvSpVj55ZurOl2XAXUpGbq5
 XRk5CESFuLQV8oqCxgWAEgFyEapI4GwJsvfl/2Er8kLoucYO1Id4mz6N33+omPhaoXfHyLSy
 dxD+CzNJqN2GdavGtobdvv/2V0wukqj86iKF8toLG2/Fia3DxMaGUxqI7GMOuiGZjXPt/et/
 qeOySghdQ7Sdpu6fWc8CJXV2mOV6DrSzc6ZVB4SmvdoruBHWWOR6YnMz01ShFE49pPucyU1h
 Av4jC62El3pdCrDOnWNFMYbbon3vABEBAAHCwn4EGAECAAkFAlYnf6QCGwICKQkQFpq3saTP
 +K7BXSAEGQECAAYFAlYnf6QACgkQd9zb2sjISdGToxAAkOjSfGxp0ulgHboUAtmxaU3viucV
 e2Hl1BVDtKSKmbIVZmEUvx9D06IijFaEzqtKD34LXD6fjl4HIyDZvwfeaZCbJbO10j3k7FJE
 QrBtpdVqkJxme/nYlGOVzcOiKIepNkwvnHVnuVDVPcXyj2wqtsU7VZDDX41z3X4xTQwY3SO1
 9nRO+f+i4RmtJcITgregMa2PcB0LvrjJlWroI+KAKCzoTHzSTpCXMJ1U/dEqyc87bFBdc+DI
 k8mWkPxsccdbs4t+hH0NoE3Kal9xtAl56RCtO/KgBLAQ5M8oToJVatxAjO1SnRYVN1EaAwrR
 xkHdd97qw6nbg9BMcAoa2NMc0/9MeiaQfbgW6b0reIz/haHhXZ6oYSCl15Knkr4t1o3I2Bqr
 Mw623gdiTzotgtId8VfLB2Vsatj35OqIn5lVbi2ua6I0gkI6S7xJhqeyrfhDNgzTHdQVHB9/
 7jnM0ERXNy1Ket6aDWZWCvM59dTyu37g3VvYzGis8XzrX1oLBU/tTXqo1IFqqIAmvh7lI0Se
 gCrXz7UanxCwUbQBFjzGn6pooEHJYRLuVGLdBuoApl/I4dLqCZij2AGa4CFzrn9W0cwm3HCO
 lR43gFyz0dSkMwNUd195FrvfAz7Bjmmi19DnORKnQmlvGe/9xEEfr5zjey1N9+mt3//geDP6
 clwKBkq0JggA+RTEAELzkgPYKJ3NutoStUAKZGiLOFMpHY6KpItbbHjF2ZKIU1whaRYkHpB2
 uLQXOzZ0d7x60PUdhqG3VmFnzXSztA4vsnDKk7x2xw0pMSTKhMafpxaPQJf494/jGnwBHyi3
 h3QGG1RjfhQ/OMTX/HKtAUB2ct3Q8/jBfF0hS5GzT6dYtj0Ci7+8LUsB2VoayhNXMnaBfh+Q
 pAhaFfRZWTjUFIV4MpDdFDame7PB50s73gF/pfQbjw5Wxtes/0FnqydfId95s+eej+17ldGp
 lMv1ok7K0H/WJSdr7UwDAHEYU++p4RRTJP6DHWXcByVlpNQ4SSAiivmWiwOt490+Ac7ATQRN
 WQbPAQgAvIoM384ZRFocFXPCOBir5m2J+96R2tI2XxMgMfyDXGJwFilBNs+fpttJlt2995A8
 0JwPj8SFdm6FBcxygmxBBCc7i/BVQuY8aC0Z/w9Vzt3Eo561r6pSHr5JGHe8hwBQUcNPd/9l
 2ynP57YTSE9XaGJK8gIuTXWo7pzIkTXfN40Wh5jeCCspj4jNsWiYhljjIbrEj300g8RUT2U0
 FcEoiV7AjJWWQ5pi8lZJX6nmB0lc69Jw03V6mblgeZ/1oTZmOepkagwy2zLDXxihf0GowUif
 GphBDeP8elWBNK+ajl5rmpAMNRoKxpN/xR4NzBg62AjyIvigdywa1RehSTfccQARAQABwsBf
 BBgBAgAJBQJNWQbPAhsMAAoJEBaat7Gkz/iuteIH+wZuRDqK0ysAh+czshtG6JJlLW6eXJJR
 Vi7dIPpgFic2LcbkSlvB8E25Pcfz/+tW+04Urg4PxxFiTFdFCZO+prfd4Mge7/OvUcwoSub7
 ZIPo8726ZF5/xXzajahoIu9/hZ4iywWPAHRvprXaim5E/vKjcTeBMJIqZtS4u/UK3EpAX59R
 XVxVpM8zJPbk535ELUr6I5HQXnihQm8l6rt9TNuf8p2WEDxc8bPAZHLjNyw9a/CdeB97m2Tr
 zR8QplXA5kogS4kLe/7/JmlDMO8Zgm9vKLHSUeesLOrjdZ59EcjldNNBszRZQgEhwaarfz46
 BSwxi7g3Mu7u5kUByanqHyA=
Organization: Baylibre
Message-ID: <190ac909-c78b-81e0-35a1-353cd24e9f44@baylibre.com>
Date:   Thu, 2 Jul 2020 17:11:25 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.8.0
MIME-Version: 1.0
In-Reply-To: <CAKMK7uHa4ajC5_SA_fFUhB-Amxcbt7T9UZ+pvRhqDeUeX9Ez6A@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi,

On 02/07/2020 16:15, Daniel Vetter wrote:
> On Thu, Jul 2, 2020 at 3:34 PM Neil Armstrong <narmstrong@baylibre.com> wrote:
>>
>> On 02/07/2020 15:18, Daniel Vetter wrote:
>>> On Thu, Jul 02, 2020 at 09:23:11AM +0000, Simon Ser wrote:
>>>> On Thursday, July 2, 2020 9:47 AM, Neil Armstrong <narmstrong@baylibre.com> wrote:
>>>>
>>>>> Finally is also adds the Scatter Memory layout, meaning the header contains IOMMU
>>>>> references to the compressed frames content to optimize memory access
>>>>> and layout.
>>>>>
>>>>> In this mode, only the header memory address is needed, thus the content
>>>>> memory organization is tied to the current producer execution and cannot
>>>>> be saved/dumped neither transferrable between Amlogic SoCs supporting this
>>>>> modifier.
>>>>
>>>> Still not sure how to handle this one, since this breaks fundamental
>>>> assumptions about modifiers.
>>>
>>> I wonder whether we should require special allocations for these, and then
>>> just outright reject mmap on these buffers. mmap on dma-buf isn't a
>>> required feature.
>>
>> Yes, it's the plan to reject mmap on these buffers, but it can't be explained
>> in the modifiers description and it's a requirement of the producer, not the
>> consumer.
> 
> Hm I think worth to add that as a note to the modifier. Just to make
> sure. And avoids questions like the one from Simon.

Something like:

 /*
  * Amlogic FBC Scatter Memory layout
  *
  * Indicates the header contains IOMMU references to the compressed
  * frames content to optimize memory access and layout.
  *
  * In this mode, only the header memory address is needed, thus the
  * content memory organization is tied to the current producer
  * execution and cannot be saved/dumped neither transferrable between
  * Amlogic SoCs supporting this modifier.
+ *
+ * Due to the nature of the layout, these buffers are not expected to
+ * be accessible by the user-space clients but only accessible by the
+ * hardware producers and consumers.
+ *
+ * The user-space clients should expect a failure while trying to mmap
+ * the DMA-BUF handle returned by the producer.
  */

Thanks,
Neil

> -Daniel
> 
>>
>>>
>>> That would make sure that userspace cannot look at them.
>>>
>>> Also I'm kinda suspecting that there's not unlimited amounts of this magic
>>> invisible storage available anyway.
>>> -Daniel
>>>
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
>