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

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Message-ID: <fbea6e6d-7721-b51d-0501-582e8446e9c9@arm.com>
Date:   Wed, 14 Aug 2019 16:49:13 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc:     linux-arch@...r.kernel.org, Olav Kongas <ok@...ecdesign.ee>,
        Gavin Li <git@...gavinli.com>, linuxppc-dev@...ts.ozlabs.org,
        Mathias Nyman <mathias.nyman@...el.com>,
        Geoff Levand <geoff@...radead.org>,
        Fabio Estevam <festevam@...il.com>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        linux-usb@...r.kernel.org, Michal Simek <michal.simek@...inx.com>,
        linux-kernel@...r.kernel.org, Tony Prisk <linux@...sktech.co.nz>,
        iommu@...ts.linux-foundation.org,
        Alan Stern <stern@...land.harvard.edu>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Minas Harutyunyan <hminas@...opsys.com>,
        Shawn Guo <shawnguo@...nel.org>, Bin Liu <b-liu@...com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 6/6] driver core: initialize a default DMA mask for
 platform device

On 11/08/2019 09:05, 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

s/object/device/

> 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.

This would be a good point to also get rid of the long-standing bodge in 
platform_device_register_full().

> 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 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)

Bikeshed: painting the generic DMA API properties as "archdata" feels a 
bit off-target :/

> +{
> +	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);

AFAICS m68k's implementation of that arch hook becomes entirely 
redundant after this change, so may as well go. That would just leave 
powerpc's actual archdata, which at a glance looks like it could 
probably be cleaned up with not *too* much trouble.

Robin.

> +};
> +
>   /**
>    * 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;
>   	u32		num_resources;
>   	struct resource	*resource;
>   
>