spi: dt-bindings: add schema listing peripheral-specific properties
Many SPI controllers need to add properties to peripheral devices. This could be the delay in clock or data lines, etc. These properties are controller specific but need to be defined in the peripheral node because they are per-peripheral and there can be multiple peripherals attached to a controller. If these properties are not added to the peripheral binding, then the dtbs check emits a warning. But these properties do not make much sense in the peripheral binding because they are controller-specific and they will just pollute every peripheral binding. So this binding is added to collect all such properties from all such controllers. Peripheral bindings should simply refer to this binding and they should be rid of the warnings. There are some limitations with this approach. Firstly, there is no way to specify required properties. The schema contains properties for all controllers and there is no way to know which controller is being used. Secondly, there is no way to restrict additional properties. Since this schema will be used with an allOf operator, additionalProperties needs to be true. In addition, the peripheral schema will have to set unevaluatedProperties: false. Despite these limitations, this appears to be the best solution to this problem that doesn't involve modifying existing tools or schema specs. Signed-off-by: Pratyush Yadav <p.yadav@ti.com> Reviewed-by: Rob Herring <robh@kernel.org> Link: https://lore.kernel.org/r/20211109181911.2251-2-p.yadav@ti.comSigned-off-by: Mark Brown <broonie@kernel.org>
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