[PATCH] net: mdio: fix -Wvoid-pointer-to-enum-cast warning

[PATCH] net: mdio: fix -Wvoid-pointer-to-enum-cast warning

[Justin Stitt]

When building with clang 18 I see the following warning:
|       drivers/net/mdio/mdio-xgene.c:338:13: warning: cast to smaller integer
|               type 'enum xgene_mdio_id' from 'const void *' [-Wvoid-pointer-to-enum-cast]
|         338 |                 mdio_id = (enum xgene_mdio_id)of_id->data;

This is due to the fact that `of_id->data` is a void* while `enum
xgene_mdio_id` has the size of an int. This leads to truncation and
possible data loss.

Link: https://github.com/ClangBuiltLinux/linux/issues/1910
Reported-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: `xgene_mdio_id` has only two fields enumerated from 1 which means
this is no data loss happening here. Either way, this patch helps the
goal of eventually enabling this warning for more builds by reducing
noise.
---
 drivers/net/mdio/mdio-xgene.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/mdio/mdio-xgene.c b/drivers/net/mdio/mdio-xgene.c
index 7aafc221b5cf..7119eb11c00d 100644
--- a/drivers/net/mdio/mdio-xgene.c
+++ b/drivers/net/mdio/mdio-xgene.c
@@ -335,7 +335,7 @@ static int xgene_mdio_probe(struct platform_device *pdev)
 
 	of_id = of_match_device(xgene_mdio_of_match, &pdev->dev);
 	if (of_id) {
-		mdio_id = (enum xgene_mdio_id)of_id->data;
+		mdio_id = (uintptr_t)of_id->data;
 	} else {
 #ifdef CONFIG_ACPI
 		const struct acpi_device_id *acpi_id;

---
base-commit: 2ccdd1b13c591d306f0401d98dedc4bdcd02b421
change-id: 20230815-void-drivers-net-mdio-mdio-xgene-e5b3b4a3343b

Best regards,
--
Justin Stitt <justinstitt@google.com>

Re: [PATCH] net: mdio: fix -Wvoid-pointer-to-enum-cast warning

[Andrew Lunn]

On Tue, Aug 15, 2023 at 08:35:59PM +0000, Justin Stitt wrote:
> When building with clang 18 I see the following warning:
> |       drivers/net/mdio/mdio-xgene.c:338:13: warning: cast to smaller integer
> |               type 'enum xgene_mdio_id' from 'const void *' [-Wvoid-pointer-to-enum-cast]
> |         338 |                 mdio_id = (enum xgene_mdio_id)of_id->data;
> 
> This is due to the fact that `of_id->data` is a void* while `enum
> xgene_mdio_id` has the size of an int. This leads to truncation and
> possible data loss.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1910
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew

Re: [PATCH] net: mdio: fix -Wvoid-pointer-to-enum-cast warning

[Russell King (Oracle)]

On Tue, Aug 15, 2023 at 10:41:39PM +0200, Andrew Lunn wrote:
> On Tue, Aug 15, 2023 at 08:35:59PM +0000, Justin Stitt wrote:
> > When building with clang 18 I see the following warning:
> > |       drivers/net/mdio/mdio-xgene.c:338:13: warning: cast to smaller integer
> > |               type 'enum xgene_mdio_id' from 'const void *' [-Wvoid-pointer-to-enum-cast]
> > |         338 |                 mdio_id = (enum xgene_mdio_id)of_id->data;
> > 
> > This is due to the fact that `of_id->data` is a void* while `enum
> > xgene_mdio_id` has the size of an int. This leads to truncation and
> > possible data loss.
> > 
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1910
> > Reported-by: Nathan Chancellor <nathan@kernel.org>
> > Signed-off-by: Justin Stitt <justinstitt@google.com>
> 
> Reviewed-by: Andrew Lunn <andrew@lunn.ch>

I wonder whether it would be better to use device_get_match_data()
here? The whole of_match_device()...acpi_match_device() dance could
become:

+	mdio_id = (uintptr_t)device_get_match_data(&pdev->dev);
	if (!mdio_id)
		return -ENODEV;

It's probably something for a follow-up patch though.

Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

Thanks!

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Re: [PATCH] net: mdio: fix -Wvoid-pointer-to-enum-cast warning

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 15 Aug 2023 20:35:59 +0000 you wrote:
> When building with clang 18 I see the following warning:
> |       drivers/net/mdio/mdio-xgene.c:338:13: warning: cast to smaller integer
> |               type 'enum xgene_mdio_id' from 'const void *' [-Wvoid-pointer-to-enum-cast]
> |         338 |                 mdio_id = (enum xgene_mdio_id)of_id->data;
> 
> This is due to the fact that `of_id->data` is a void* while `enum
> xgene_mdio_id` has the size of an int. This leads to truncation and
> possible data loss.
> 
> [...]

Here is the summary with links:
  - net: mdio: fix -Wvoid-pointer-to-enum-cast warning
    https://git.kernel.org/netdev/net-next/c/f3add6dec36d

You are awesome, thank you!
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