linux-kernel - Re: [PATCH net v2] nui: Fix dma_mapping

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Message-ID: <20250630170906.GN41770@horms.kernel.org>
Date: Mon, 30 Jun 2025 18:09:06 +0100
From: Simon Horman <horms@...nel.org>
To: Thomas Fourier <fourier.thomas@...il.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Jonathan Currier <dullfire@...oo.com>,
	Uwe Kleine-König <u.kleine-koenig@...libre.com>,
	Shuah Khan <shuah@...nel.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] nui: Fix dma_mapping_error() check

On Mon, Jun 30, 2025 at 10:36:43AM +0200, Thomas Fourier wrote:
> dma_map_XXX() functions return values DMA_MAPPING_ERROR as error values
> which is often ~0.  The error value should be tested with
> dma_mapping_error().
> 
> This patch creates a new function in niu_ops to test if the mapping
> failed.  The test is fixed in niu_rbr_add_page(), added in
> niu_start_xmit() and the successfully mapped pages are unmaped upon error.
> 
> Fixes: ec2deec1f352 ("niu: Fix to check for dma mapping errors.")

I think it fixes a bit more than that.
But perhaps the above tag is sufficient.

> Signed-off-by: Thomas Fourier <fourier.thomas@...il.com>

Overall this looks good to me, thanks for the update.

Reviewed-by: Simon Horman <horms@...nel.org>

> ---
>  drivers/net/ethernet/sun/niu.c | 31 ++++++++++++++++++++++++++++++-
>  drivers/net/ethernet/sun/niu.h |  4 ++++
>  2 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/sun/niu.c b/drivers/net/ethernet/sun/niu.c

...

> @@ -10019,6 +10042,11 @@ static void niu_phys_unmap_single(struct device *dev, u64 dma_address,
>  	/* Nothing to do.  */
>  }
>  
> +static int niu_phys_mapping_error(struct device *dev, u64 dma_address)
> +{
> +	return false;

No need to resend just because of this, but
from a type PoV this should probably be:

	return 0;

> +}
> +
>  static const struct niu_ops niu_phys_ops = {
>  	.alloc_coherent	= niu_phys_alloc_coherent,
>  	.free_coherent	= niu_phys_free_coherent,

...