linux-kernel - Re: [PATCH] net: mvpp2: avoid bouncing buffers

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Date:   Sat, 1 Sep 2018 21:10:36 -0500
From:   Brian Brooks <brian.brooks@...aro.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     David Miller <davem@...emloft.net>, antoine.tenart@...tlin.com,
        maxime.chevallier@...tlin.com, ymarkman@...vell.com,
        stefanc@...vell.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bjorn.topel@...el.com,
        brian.brooks@....com
Subject: Re: [PATCH] net: mvpp2: avoid bouncing buffers

On 08/27 08:48:43, Christoph Hellwig wrote:
> WE should basically never have dev->dma_mask = &dev->coherent_dma_mask,
> so until that is the case you are doctoring around the symptoms and
> not the problem.
> 
> Does the patch below help your case?

Yes. Just tested it. Works great.

I see how this patch addresses the issue in the platform code instead of
the driver code. Thanks.

> ----
> From 6294e0e330851ee06e66ab85b348f1d92d375d7a Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@....de>
> Date: Mon, 27 Aug 2018 17:23:24 +0200
> Subject: driver core: initialize a default DMA mask for platform device
> 
> We still treat devices without a DMA mask as defaulting to 32-bits for
> both mask, but a few releases ago we've started warning about such
> cases, as they require special cases to work around this sloppyness.
> Add a dma_mask field to struct platform_object so that we can initialize
> the dma_mask pointer in struct device and initialize both masks to
> 32-bits by default.  Architectures can still override this in
> arch_setup_pdev_archdata if needed.
> 
> Note that the code looks a little odd with the various conditionals
> because we have to support platform_device structures that are
> statically allocated.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  drivers/base/platform.c         | 15 +++++++++++++--
>  include/linux/platform_device.h |  1 +
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index dff82a3c2caa..baf4b06cf2d9 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -225,6 +225,17 @@ struct platform_object {
>  	char name[];
>  };
>  
> +static void setup_pdev_archdata(struct platform_device *pdev)
> +{
> +	if (!pdev->dev.coherent_dma_mask)
> +		pdev->dev.coherent_dma_mask = DMA_BIT_MASK(32);
> +	if (!pdev->dma_mask)
> +		pdev->dma_mask = DMA_BIT_MASK(32);
> +	if (!pdev->dev.dma_mask)
> +		pdev->dev.dma_mask = &pdev->dma_mask;
> +	arch_setup_pdev_archdata(pdev);
> +};
> +
>  /**
>   * platform_device_put - destroy a platform device
>   * @pdev: platform device to free
> @@ -271,7 +282,7 @@ struct platform_device *platform_device_alloc(const char *name, int id)
>  		pa->pdev.id = id;
>  		device_initialize(&pa->pdev.dev);
>  		pa->pdev.dev.release = platform_device_release;
> -		arch_setup_pdev_archdata(&pa->pdev);
> +		setup_pdev_archdata(&pa->pdev);
>  	}
>  
>  	return pa ? &pa->pdev : NULL;
> @@ -472,7 +483,7 @@ EXPORT_SYMBOL_GPL(platform_device_del);
>  int platform_device_register(struct platform_device *pdev)
>  {
>  	device_initialize(&pdev->dev);
> -	arch_setup_pdev_archdata(pdev);
> +	setup_pdev_archdata(pdev);
>  	return platform_device_add(pdev);
>  }
>  EXPORT_SYMBOL_GPL(platform_device_register);
> diff --git a/include/linux/platform_device.h b/include/linux/platform_device.h
> index 1a9f38f27f65..d84ec1de6022 100644
> --- a/include/linux/platform_device.h
> +++ b/include/linux/platform_device.h
> @@ -25,6 +25,7 @@ struct platform_device {
>  	int		id;
>  	bool		id_auto;
>  	struct device	dev;
> +	dma_addr_t	dma_mask;

Hmm.. should struct device use dma_addr_t instead of u64 for masks too?

>  	u32		num_resources;
>  	struct resource	*resource;
>  
> -- 
> 2.18.0
>