Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Received-SPF: Pass (protection.outlook.com: domain of xilinx.com designates
 149.199.62.198 as permitted sender) receiver=protection.outlook.com;
 client-ip=149.199.62.198; helo=xsj-pvapexch02.xlnx.xilinx.com;
Envelope-to: seanga2@gmail.com,
 zajec5@gmail.com,
 robh+dt@kernel.org,
 trini@konsulko.com,
 sjg@chromium.org,
 srinivas.kandagatla@linaro.org,
 krzysztof.kozlowski@canonical.com,
 ricardo@foundries.io,
 jorge@foundries.io,
 devicetree@vger.kernel.org,
 u-boot@lists.denx.de,
 linux-kernel@vger.kernel.org,
 rafal@milecki.pl
Message-ID: <2def78a6-afbf-7534-358c-9515abf1b68e@xilinx.com>
Date:   Tue, 15 Feb 2022 16:02:34 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.6.0
Subject: Re: [PATCH] dt-bindings: nvmem: add U-Boot environment variables
 binding
Content-Language: en-US
To:     Sean Anderson <seanga2@gmail.com>,
        Michal Simek <michal.simek@xilinx.com>,
        =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <zajec5@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Tom Rini <trini@konsulko.com>, Simon Glass <sjg@chromium.org>
CC:     Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        Ricardo Salveti <ricardo@foundries.io>,
        Jorge Ramirez-Ortiz <jorge@foundries.io>,
        <devicetree@vger.kernel.org>, <u-boot@lists.denx.de>,
        <linux-kernel@vger.kernel.org>,
        =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <rafal@milecki.pl>
References: <20220215134925.32691-1-zajec5@gmail.com>
 <193f9354-5e1d-def8-c8ab-fbe88d8d9b8f@xilinx.com>
 <6679b98e-f5f0-8608-a36c-c0c41fb5ea6f@gmail.com>
From:   Michal Simek <michal.simek@xilinx.com>
In-Reply-To: <6679b98e-f5f0-8608-a36c-c0c41fb5ea6f@gmail.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 8bit
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Feb 2022 15:02:42.0371
 (UTC)
X-MS-Exchange-CrossTenant-Network-Message-Id: f06017ce-1f0c-4917-4c70-08d9f094372f
X-MS-Exchange-CrossTenant-Id: 657af505-d5df-48d0-8300-c31994686c5c
X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=657af505-d5df-48d0-8300-c31994686c5c;Ip=[149.199.62.198];Helo=[xsj-pvapexch02.xlnx.xilinx.com]
X-MS-Exchange-CrossTenant-AuthSource: DM3NAM02FT016.eop-nam02.prod.protection.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Anonymous
X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR02MB7348
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,
        SPF_HELO_PASS,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 2/15/22 15:57, Sean Anderson wrote:
> On 2/15/22 9:02 AM, Michal Simek wrote:
>>
>>
>> On 2/15/22 14:49, Rafał Miłecki wrote:
>>> From: Rafał Miłecki <rafal@milecki.pl>
>>>
>>> U-Boot uses environment variables for storing device setup data on
>>> flash. That data usually needs to be accessed by a bootloader, kernel
>>> and often user-space.
>>>
>>> This binding allows describing environment data location and its format
>>> clearly. In some/many cases it should be cleaner than hardcoding &
>>> duplicating that info in multiple places. Bootloader & kernel can share
>>> DTS and user-space can try reading it too or just have correct data
>>> exposed by a kernel.
>>>
>>> Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
>>> ---
>>>   .../devicetree/bindings/nvmem/u-boot,env.yaml | 58 +++++++++++++++++++
>>>   MAINTAINERS                                   |  5 ++
>>>   2 files changed, 63 insertions(+)
>>>   create mode 100644 Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
>>>
>>> diff --git a/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml 
>>> b/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
>>> new file mode 100644
>>> index 000000000000..a2b3a9b88eb8
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/nvmem/u-boot,env.yaml
>>> @@ -0,0 +1,58 @@
>>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/nvmem/u-boot,env.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: U-Boot environment variables
>>> +
>>> +description: |
>>> +  U-Boot uses environment variables to store device parameters and
>>> +  configuration. They may be used for booting process, setup or keeping end 
>>> user
>>> +  info.
>>> +
>>> +  Data is stored on flash in a U-Boot specific format (header and NUL separated
>>> +  key-value pairs).
>>> +
>>> +  This binding allows specifying data location and used format.
>>> +
>>> +maintainers:
>>> +  - Rafał Miłecki <rafal@milecki.pl>
>>> +
>>> +allOf:
>>> +  - $ref: nvmem.yaml#
>>> +
>>> +properties:
>>> +  compatible:
>>> +    oneOf:
>>> +      - description: A standalone env data block
>>> +        const: u-boot,env
>>> +      - description: Two redundant blocks with active one flagged
>>> +        const: u-boot,env-redundant-bool
>>> +      - description: Two redundant blocks with active having higher counter
>>> +        const: u-boot,env-redundant-count
>>
>> I am not convinced that this is the best way how to do it. Because in u-boot 
>> implementation you would have to enable MTD partitions to get there.
>> And the whole parsing will take a lot of time.
>>
>> I think the way how I think this can be handled is.
>>
>> # I don't think that discussion with Simon was finished.
>> But for example (chosen or firmware node)
>> chosen {
>>      u-boot {
>>          u-boot,env = <&qspi &part0>;
>>          u-boot,env-redundant = <&qspi &part1>;
>>          #or
>>          u-boot,env = <&qspi 0 40000>;
>>          u-boot,env-redundant = <&qspi 40000 40000>;
> 
> What about when the environment is on top of UBI?

I expect we should list all possible combinations and cover them here.

> 
>>          #or
>>          u-boot,env = <&mmc 0 0 10000>; #device/start/size - raw mode
>>          u-boot,env = <&mmc 0 1>; # device/partition - as file to FS
> 
> For emmc at least you will need another cell for the hardware partition.
> And of course, you can name the environment file whatever you want, so
> that needs to be recorded as well.
> 
> IMO to do this properly you'd need to have a property corresponding to
> each of the major configs in the env menu.

Agree 100%. I just wanted to share how I think this should be done.
At the end we should be able to describe any combination in generic way.

Thanks,
Michal