[PATCH v7 1/2] spi: Unify error codes by replacing -ENOTSUPP with -EOPNOTSUPP

[Florian Fainelli]

On 11/28/2023 10:43 PM, AceLan Kao wrote:
> From: "Chia-Lin Kao (AceLan)" <acelan.kao at canonical.com>
> 
> This commit updates the SPI subsystem, particularly affecting "SPI MEM"
> drivers and core parts, by replacing the -ENOTSUPP error code with
> -EOPNOTSUPP.
> 
> The key motivations for this change are as follows:
> 1. The spi-nor driver currently uses EOPNOTSUPP, whereas calls to spi-mem
> might return ENOTSUPP. This update aims to unify the error reporting
> within the SPI subsystem for clarity and consistency.
> 
> 2. The use of ENOTSUPP has been flagged by checkpatch as inappropriate,
> mainly being reserved for NFS-related errors. To align with kernel coding
> standards and recommendations, this change is being made.
> 
> 3. By using EOPNOTSUPP, we provide more specific context to the error,
> indicating that a particular operation is not supported. This helps
> differentiate from the more generic ENOTSUPP error, allowing drivers to
> better handle and respond to different error scenarios.
> 
> Risks and Considerations:
> While this change is primarily intended as a code cleanup and error code
> unification, there is a minor risk of breaking user-space applications
> that rely on specific return codes for unsupported operations. However,
> this risk is considered low, as such use-cases are unlikely to be common
> or critical. Nevertheless, developers and users should be aware of this
> change, especially if they have scripts or tools that specifically handle
> SPI error codes.
> 
> This commit does not introduce any functional changes to the SPI subsystem
> or the affected drivers.
> 
> Signed-off-by: Chia-Lin Kao (AceLan) <acelan.kao at canonical.com>

This patch breaks SPI probing with spi-bcm-qspi.c on v6.8 and beyond:

[    2.196300] brcmstb_qspi f0440920.qspi: using bspi-mspi mode
[    2.210295] spi-nor: probe of spi1.0 failed with error -95

I am still going down drivers/mtd/spi-nor/core.c to figure out where 
this broke.
-- 
Florian
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