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

From: Robin Murphy <robin.murphy@arm.com>
To: Christoph Hellwig <hch@lst.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Maxime Chevallier <maxime.chevallier@bootlin.com>
Cc: linux-arch@vger.kernel.org, Olav Kongas <ok@artecdesign.ee>,
	Gavin Li <git@thegavinli.com>,
	linuxppc-dev@lists.ozlabs.org,
	Mathias Nyman <mathias.nyman@intel.com>,
	Geoff Levand <geoff@infradead.org>,
	Fabio Estevam <festevam@gmail.com>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	linux-usb@vger.kernel.org, Michal Simek <michal.simek@xilinx.com>,
	linux-kernel@vger.kernel.org, Tony Prisk <linux@prisktech.co.nz>,
	iommu@lists.linux-foundation.org,
	Alan Stern <stern@rowland.harvard.edu>,
	NXP Linux Team <linux-imx@nxp.com>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Minas Harutyunyan <hminas@synopsys.com>,
	Shawn Guo <shawnguo@kernel.org>, Bin Liu <b-liu@ti.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 6/6] driver core: initialize a default DMA mask for platform device
Date: Wed, 14 Aug 2019 16:49:13 +0100	[thread overview]
Message-ID: <fbea6e6d-7721-b51d-0501-582e8446e9c9@arm.com> (raw)
In-Reply-To: <20190811080520.21712-7-hch@lst.de>

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@lst.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;
>   
> 