Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v3 06/19] dt-bindings: memory: tegra: Squash tegra20-gart
 into tegra20-mc
From:   Dmitry Osipenko <digetx@gmail.com>
To:     Rob Herring <robh@kernel.org>
Cc:     Thierry Reding <thierry.reding@gmail.com>,
        Joerg Roedel <joro@8bytes.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Jonathan Hunter <jonathanh@nvidia.com>,
        iommu@lists.linux-foundation.org, devicetree@vger.kernel.org,
        linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20180818155430.5586-1-digetx@gmail.com>
 <20180818155430.5586-7-digetx@gmail.com> <20180820191209.GA28618@bogus>
 <b46cac22-9b31-9aa7-7eca-4725156346bb@gmail.com>
Openpgp: preference=signencrypt
Autocrypt: addr=digetx@gmail.com; prefer-encrypt=mutual; keydata=
 xsBNBFpX5TwBCADQhg+lBnTunWSPbP5I+rM9q6EKPm5fu2RbqyVAh/W3fRvLyghdb58Yrmjm
 KpDYUhBIZvAQoFLEL1IPAgJBtmPvemO1XUGPxfYNh/3BlcDFBAgERrI3BfA/6pk7SAFn8u84
 p+J1TW4rrPYcusfs44abJrn8CH0GZKt2AZIsGbGQ79O2HHXKHr9V95ZEPWH5AR0UtL6wxg6o
 O56UNG3rIzSL5getRDQW3yCtjcqM44mz6GPhSE2sxNgqureAbnzvr4/93ndOHtQUXPzzTrYB
 z/WqLGhPdx5Ouzn0Q0kSVCQiqeExlcQ7i7aKRRrELz/5/IXbCo2O+53twlX8xOps9iMfABEB
 AAHNIkRtaXRyeSBPc2lwZW5rbyA8ZGlnZXR4QGdtYWlsLmNvbT7CwJQEEwEIAD4WIQSczHcO
 3uc4K1eb3yvTNNaPsNRzvAUCWlflPAIbAwUJA8JnAAULCQgHAgYVCgkICwIEFgIDAQIeAQIX
 gAAKCRDTNNaPsNRzvFjTCACqAh1M9/YPq73/ai5h2ExDquTgJnjegL8KL2yHL3G+XINwzN5E
 nPI7esoYm+zVWDJbv3UuRqylpookLNSRA01yyvkaMcipB/B128UnqmUiGRqezj9QE20yIauo
 uHRuwHPE2q+UkfUhRX9iuOaEyQtZDiCa0myMjmRkJ+Z8ZetclEPG8dYZu47w04phuMlu1QAt
 a0gkZOaMKvXgj21ushALS6nYnvm7HiIPQXfnEXThartatRvFdmbG4PCn0IoICkQBizwJtXrL
 HEjELIFap0M8krVJlUoZTFaZnaZkGpUDWikeFtAuie2KuIxmVBYPM4X7pM3eP3AVvIPGS7EE
 UUFuzsBNBFpX5TwBCADFNDou220thijaLLGaQsebWjzc/gPRxMixIpk856MRyRaQin+IbGD6
 YskMb5ZSD3nS88LIKNfY4MMH0LwfYztI++ICG2vdFLkbBt78E+LqEa+kZ9072l4W5KO3mWQo
 +jMfxXbpgGlc7iuEReDgl8iyZ27r51kSW665CYvvu2YJhLqgdj6QM1lN2D1UnhEhkkU+pRAj
 1rJVOxdfJaQNQS4+204p3TrURovzNGkN/brqakpNIcqGOAGQqb8F0tuwwuP7ERq/BzDNkbdr
 qJOrVC/wkHRq1jfabQczWKf8MwYOvivR3HY8d3CpSQxmUXDtdOWfg0XGm1dxYnVfqPjuJaZt
 ABEBAAHCwHwEGAEIACYWIQSczHcO3uc4K1eb3yvTNNaPsNRzvAUCWlflPAIbDAUJA8JnAAAK
 CRDTNNaPsNRzvJzuB/9d+sxcwHbO8ZDcgaLX9N+bXFqN9fIRVmBUyWa+qqTSREA4uVAtYcRT
 lfPE2OQ7aMFxaYPwo+/z5SLpu8HcEhN/FG9uIkfYwK0mdCO0vgvlfvBJm4VHe7C6vyAeEPJQ
 DKbBvdgeqFqO+PsLkk2sawF/9sontMJ5iFfjNDj4UeAo4VsdlduTBZv5hHFvIbv/p7jKH6OT
 90FsgUSVbShh7SH5OzAcgqSy4kxuS1AHizWo6P3f9vei987LZWTyhuEuhJsOfivDsjKIq7qQ
 c5eR+JJtyLEA0Jt4cQGhpzHtWB0yB3XxXzHVa4QUp00BNVWyiJ/t9JHT4S5mdyLfcKm7ddc9
Message-ID: <4538309b-fcb3-73ee-04e3-6cefcedd376d@gmail.com>
Date:   Mon, 20 Aug 2018 22:35:54 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <b46cac22-9b31-9aa7-7eca-4725156346bb@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

On 20.08.2018 22:27, Dmitry Osipenko wrote:
> On 20.08.2018 22:12, Rob Herring wrote:
>> On Sat, Aug 18, 2018 at 06:54:17PM +0300, Dmitry Osipenko wrote:
>>> Splitting GART and Memory Controller wasn't a good decision that was made
>>> back in the day. Given that the GART driver hasn't ever been used by
>>> anything in the kernel, we decided that it will be better to correct the
>>> mistakes of the past and merge two bindings into a single one. In a result
>>
>> As a result...
>>
>>> there is a DT ABI change for the Memory Controller that allows not to
>>> break newer kernels using older DT by introducing a new required property,
>>> the memory clock. Adding the new clock property also puts the tegra20-mc
>>> binding in line with the bindings of the later Tegra generations.
>>
>> I don't understand this part. It looks to me like you are breaking 
>> compatibility. The driver failing to probe with an old DT is okay?
> 
> Yes, DT compatibility is broken. New driver won't probe/load with the old DT,
> that's what we want.
> 
>> OS's like OpenSUSE use new DTs with older kernel versions, so you should 
>> consider how to not break them as well. I guess if all this is optional 
>> or has been unused, then there shouldn't be a problem.
> 
> That's interesting.. Memory Controller isn't optional, I guess we could change
> compatible to "nvidia,tegra20-mc-gart".

* I meant it's not optional in a sense that it's enabled in kernels config by
default and driver is functional, but it's okay if MC driver will stop to probe
with older kernels as it is used only for reporting memory errors.