Subject: Re: [PATCH 6/6] driver core: initialize a default DMA mask for platform device

From: Greg Kroah-Hartman <[email-masked]>
Date: Thu, 15 Aug 2019 15:03:25 +0200

On Sun, Aug 11, 2019 at 10:05:20AM +0200, Christoph Hellwig wrote:
> 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 <[email-masked]>
> ---
>  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 ec974ba9c0c4..b216fcb0a8af 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -264,6 +264,17 @@ 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
> @@ -310,7 +321,7 @@ 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;
> @@ -512,7 +523,7 @@ 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 9bc36b589827..a2abde2aef25 100644
> --- a/include/linux/platform_device.h
> +++ b/include/linux/platform_device.h
> @@ -24,6 +24,7 @@ struct platform_device {
>  	int		id;
>  	bool		id_auto;
>  	struct device	dev;
> +	u64		dma_mask;

Why is the dma_mask in 'struct device' which is part of this structure,
not sufficient here?  Shouldn't the "platform" be setting that up
correctly already in the "archdata" type callback?

confused,

greg k-h