netdev - Re: [PATCH net] net: phy: qt2025: Fix warning: unused import DeviceId

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Message-Id: <20240920.135339.42277957091918023.fujita.tomonori@gmail.com>
Date: Fri, 20 Sep 2024 13:53:39 +0000 (UTC)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: aliceryhl@...gle.com
Cc: fujita.tomonori@...il.com, netdev@...r.kernel.org,
 rust-for-linux@...r.kernel.org, andrew@...n.ch, tmgross@...ch.edu,
 lkp@...el.com
Subject: Re: [PATCH net] net: phy: qt2025: Fix warning: unused import
 DeviceId

Hi,

On Thu, 19 Sep 2024 08:17:42 +0200
Alice Ryhl <aliceryhl@...gle.com> wrote:

> On Thu, Sep 19, 2024 at 6:39 AM FUJITA Tomonori
> <fujita.tomonori@...il.com> wrote:
>>
>> Fix the following warning when the driver is compiled as built-in:
>>
>> >> warning: unused import: `DeviceId`
>>    --> drivers/net/phy/qt2025.rs:18:5
>>    |
>>    18 |     DeviceId, Driver,
>>    |     ^^^^^^^^
>>    |
>>    = note: `#[warn(unused_imports)]` on by default
>>
>> device_table in module_phy_driver macro is defined only when the
>> driver is built as module. Use an absolute module path in the macro
>> instead of importing `DeviceId`.
>>
>> Reported-by: kernel test robot <lkp@...el.com>
>> Closes: https://lore.kernel.org/oe-kbuild-all/202409190717.i135rfVo-lkp@intel.com/
>> Signed-off-by: FUJITA Tomonori <fujita.tomonori@...il.com>
> 
> It may be nice to change the macro to always use the expression so
> that this warning doesn't happen again.

Like the C code does, a valuable is defined only when the driver is
built as module because the valuable is used to create the information
for module loading. So the macro adds `#[cfg(MODULE)]` like the
following:

#[cfg(MODULE)]
#[no_mangle]
static __mod_mdio__phydev_device_table: [::kernel::bindings::mdio_device_id; 2] = [
    ::kernel::bindings::mdio_device_id {
        phy_id: 0x00000001,
        phy_id_mask: 0xffffffff,
    },
    ::kernel::bindings::mdio_device_id {
        phy_id: 0,
        phy_id_mask: 0,
    },
];

We can remove `#[cfg(MODULE)]` however an unused valuable to added to
the kernel image when the driver is compiled as built-in. Seems that
with `#[no_mangle]`, the compiler doesn't give a warning about unused
valuable though.

Is there a nice way to handle such case?

> Anyway, that is a separate issue.
> 
> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>

Thanks a lot!