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

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Date:   Thu, 15 Aug 2019 16:05:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Gavin Li <git@...gavinli.com>,
        Laurentiu Tudor <laurentiu.tudor@....com>,
        Minas Harutyunyan <hminas@...opsys.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Geoff Levand <geoff@...radead.org>,
        Michal Simek <michal.simek@...inx.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Olav Kongas <ok@...ecdesign.ee>,
        Tony Prisk <linux@...sktech.co.nz>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Bin Liu <b-liu@...com>, linux-arm-kernel@...ts.infradead.org,
        linux-usb@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        iommu@...ts.linux-foundation.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] driver core: initialize a default DMA mask for
 platform device

On Thu, Aug 15, 2019 at 03:38:12PM +0200, Christoph Hellwig wrote:
> 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.

Ah, missed that, sorry.  Ok, no objection from me.  Might as well respin
this series and I can queue it up after 5.3-rc5 is out (which will have
your first 2 patches in it.)

thanks,

greg k-h