linux-kernel - Re: [PATCH v4] nvmem: core: skip child nodes not matching binding

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Date:   Fri, 22 Jan 2021 15:27:52 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Ahmad Fatoum <a.fatoum@...gutronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     Kamel Bouhara <kamel.bouhara@...tlin.com>, ceggers@...i.de,
        kernel@...gutronix.de, Rob Herring <robh+dt@...nel.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] nvmem: core: skip child nodes not matching binding



On 18/01/2021 13:24, Ahmad Fatoum wrote:
> The nvmem cell binding applies to all eeprom child nodes matching
> "^.*@[0-9a-f]+$" without taking a compatible into account.
> 
> Linux drivers, like at24, are even more extensive and assume
> _all_ at24 eeprom child nodes to be nvmem cells since e888d445ac33
> ("nvmem: resolve cells from DT at registration time").
> 
> Since df5f3b6f5357 ("dt-bindings: nvmem: stm32: new property for
> data access"), the additionalProperties: True means it's Ok to have
> other properties as long as they don't match "^.*@[0-9a-f]+$".
> 
> The barebox bootloader extends the MTD partitions binding to
> EEPROM and can fix up following device tree node:
> 
>    &eeprom {
>      partitions {
>        compatible = "fixed-partitions";
>      };
>    };
> 
> This is allowed binding-wise, but drivers using nvmem_register()
> like at24 will fail to parse because the function expects all child
> nodes to have a reg property present. This results in the whole
> EEPROM driver probe failing despite the device tree being correct.
> 
> Fix this by skipping nodes lacking a reg property instead of
> returning an error. This effectively makes the drivers adhere
> to the binding because all nodes with a unit address must have
> a reg property and vice versa.
> 
> Fixes: e888d445ac33 ("nvmem: resolve cells from DT at registration time").
> Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
> 
> ---
> Previous Discussion: https://lore.kernel.org/lkml/20200428111829.2215-1-a.fatoum@pengutronix.de/
> v1:
>    - Ignore all nodes with a unit address (i.e. contain @)
> v1 -> v2:
>    - use ->full_name instead of ->name as to not break existing correct
>      cells (Christian)
> v2 -> v3:
>    - use optional compatible property to weed out nodes instead of name
>    - extend binding documentation (Srini)
> v3 -> v4:
>    - drop optional nvmem-cell compatible because it's redundant (Rob)
>    - Make driver adhere to binding instead of changing binding
> 
> As review feedback on v3, Rob suggested moving nvmem cells into a
> separate MTD partition. This sound good for people who want MTD
> partitions and nvmem to coexist, but my problem described above where
> MTD partitions are already fixed up top level into an EEPROM node isn't
> solved by this. Revisiting the issue, I think the correct way forward is
> along the lines of v1 & v2, where the driver is fixed to actually adhere
> to the existing binding. Srini didn't like string matching for @ in driver
> code, so I now check for presence of reg instead. They are equivalent
> per device tree specification. From v0.3:
> 
>    "The unit-address must match the first address specified in the
>    reg property of the node. If the node has no reg property, the
>    @unit-address must be omitted"...
> 
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: devicetree@...r.kernel.org
> ---
>   drivers/nvmem/core.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)


Applied thanks,

--srini

> 
> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> index 177f5bf27c6d..f114df55f403 100644
> --- a/drivers/nvmem/core.c
> +++ b/drivers/nvmem/core.c
> @@ -682,7 +682,9 @@ static int nvmem_add_cells_from_of(struct nvmem_device *nvmem)
>   
>   	for_each_child_of_node(parent, child) {
>   		addr = of_get_property(child, "reg", &len);
> -		if (!addr || (len < 2 * sizeof(u32))) {
> +		if (!addr)
> +			continue;
> +		if (len < 2 * sizeof(u32)) {
>   			dev_err(dev, "nvmem: invalid reg on %pOF\n", child);
>   			return -EINVAL;
>   		}
>