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Date:   Mon, 27 Aug 2018 10:11:52 -0700
From:   Guenter Roeck <linux@roeck-us.net>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Linux 4.19-rc1
Message-ID: <20180827171152.GA2705@roeck-us.net>
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 <20180827154641.GA17201@infradead.org>
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On Mon, Aug 27, 2018 at 08:46:41AM -0700, Christoph Hellwig wrote:
> > sparc:
> > 
> > WARNING: CPU: 0 PID: 1 at ./include/linux/dma-mapping.h:516 esp_sbus_probe+0x408/0x6e8
> > WARNING: CPU: 0 PID: 1 at ./include/linux/dma-mapping.h:516 sparc_lance_probe_one+0x428/0x4f
> > 
> > Missing initialization of coherent_dma_mask in the respective drivers.
> > 
> > ---
> > Each platform driver instantiated through a devicetree node now generates
> > the following warning:
> > 
> > esp ffd38e00: DMA mask not set
> > 
> > It isn't a traceback so it may fly under the radar. There is nothing the
> > drivers can do about it; the message is generated by the core before the
> > driver probe function is called. No idea what a correct fix might be.
> 
> Both of these should probably be fixed by something like the patch
> below:
> 
> ---
> From 6294e0e330851ee06e66ab85b348f1d92d375d7a Mon Sep 17 00:00:00 2001
> From: Christoph Hellwig <hch@lst.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@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 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;

When building sparc32 images, this results in the following
error.

drivers/base/platform.c: In function 'setup_pdev_archdata':
drivers/base/platform.c:235:22: error: assignment from incompatible pointer type [-Werror=incompatible-pointer-types]
   pdev->dev.dma_mask = &pdev->dma_mask;

pdev->dev.dma_mask is u64 *, pdev->dma_mask is dma_addr_t which in turn
is either u32 or u64 depending on the architecture.

> +++ 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;

... so this will have to be u64, or the pointer in struct device would
have to be fixed.

However, even changing the definition to u64 does not help: The warnings
are still reported. This is because setup_pdev_archdata() is not called
for any of the affected devices. That is kind of interesting since it
means that arch_setup_pdev_archdata() won't be called for those devices
either.

Guenter