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From: Christoph Hellwig <hch@lst.de>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Christoph Hellwig <hch@lst.de>,
	Maxime Chevallier <maxime.chevallier@bootlin.com>,
	Gavin Li <git@thegavinli.com>,
	Laurentiu Tudor <laurentiu.tudor@nxp.com>,
	Minas Harutyunyan <hminas@synopsys.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Geoff Levand <geoff@infradead.org>,
	Michal Simek <michal.simek@xilinx.com>,
	Shawn Guo <shawnguo@kernel.org>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	Pengutronix Kernel Team <kernel@pengutronix.de>,
	Fabio Estevam <festevam@gmail.com>,
	NXP Linux Team <linux-imx@nxp.com>,
	Olav Kongas <ok@artecdesign.ee>,
	Tony Prisk <linux@prisktech.co.nz>,
	Mathias Nyman <mathias.nyman@intel.com>, Bin Liu <b-liu@ti.com>,
	linux-arm-kernel@lists.infradead.org, linux-usb@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, iommu@lists.linux-foundation.org,
	linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/6] driver core: initialize a default DMA mask for platform device
Date: Thu, 15 Aug 2019 15:38:12 +0200
Message-ID: <20190815133812.GF12036@lst.de> (raw)
In-Reply-To: <20190815130325.GB17065@kroah.com>

On Thu, Aug 15, 2019 at 03:03:25PM +0200, Greg Kroah-Hartman wrote:
> > --- 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?

Becaus the dma_mask in struct device is a pointer that needs to point
to something, and this is the best space we can allocate for 'something'.
m68k and powerpc currently do something roughly equivalent at the moment,
while everyone else just has horrible, horrible hacks.  As mentioned in
the changelog the intent of this patch is that we treat platform devices
like any other bus, where the bus allocates the space for the dma_mask.
The long term plan is to eventually kill that weird pointer indirection
that doesn't help anyone, but for that we need to sort out the basics
first.

  reply index

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-11  8:05 next take at setting up a dma mask by default for platform devices Christoph Hellwig
2019-08-11  8:05 ` [PATCH 1/6] usb: don't create dma pools for HCDs with a localmem_pool Christoph Hellwig
2019-08-11  8:05 ` [PATCH 2/6] usb: add a hcd_uses_dma helper Christoph Hellwig
2019-08-11  8:05 ` [PATCH 3/6] usb: add a HCD_DMA flag instead of guestimating DMA capabilities Christoph Hellwig
2019-08-12 11:57   ` Christoph Hellwig
2019-08-11  8:05 ` [PATCH 4/6] usb/max3421: remove the dummy {un,}map_urb_for_dma methods Christoph Hellwig
2019-08-11  8:05 ` [PATCH 5/6] dma-mapping: remove is_device_dma_capable Christoph Hellwig
2019-08-11  8:05 ` [PATCH 6/6] driver core: initialize a default DMA mask for platform device Christoph Hellwig
2019-08-14 15:49   ` Robin Murphy
2019-08-15 13:32     ` Christoph Hellwig
2019-08-15 13:03   ` Greg Kroah-Hartman
2019-08-15 13:38     ` Christoph Hellwig [this message]
2019-08-15 14:05       ` Greg Kroah-Hartman
2019-08-15 13:23 ` next take at setting up a dma mask by default for platform devices Greg Kroah-Hartman
2019-08-15 13:25   ` Christoph Hellwig
2019-08-15 14:05     ` Greg Kroah-Hartman
2019-08-15 14:39     ` Alan Stern
2019-08-16  6:24 next take at setting up a dma mask by default for platform devices v2 Christoph Hellwig
2019-08-16  6:24 ` [PATCH 6/6] driver core: initialize a default DMA mask for platform device Christoph Hellwig
2019-08-16  7:39   ` Geert Uytterhoeven

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