linux-kernel - Re: [PATCH] driver core: platform: Allow using a dedicated dma_mask for platform

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Message-ID: <20190703172115.GA22034@infradead.org>
Date:   Wed, 3 Jul 2019 10:21:16 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Russell King <linux@...linux.org.uk>,
        David Miller <davem@...emloft.net>, brian.brooks@...aro.org,
        linux-kernel@...r.kernel.org,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        thomas.petazzoni@...tlin.com, linux-arm-kernel@...ts.infradead.org,
        nadavh@...vell.com, stefanc@...vell.com,
        Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: [PATCH] driver core: platform: Allow using a dedicated dma_mask
 for platform_device

On Mon, Jul 01, 2019 at 01:24:39PM +0200, Maxime Chevallier wrote:
> I agree that this the real solution, it just seemed a bit overwhelming
> to me. I'll be happy to help with this though, now that you took a big
> first step.

I think the first step is to resurrect my original patch to default
to a 32-bit DMA mask for platform devices, as that will cut a lot
of crap from the platform device declarations.

IIRC the problem back then was that USB uses the fact that a DMA
mask exist to decide if it uses a DMA vs PIO path in the HCD core.

So I'll need some help from Greg or other USB folks to clean that up,
after that we can try to apply my patch again (preferably early in
the next merge window), and once that sticks clean up all the 32-bit
dma mask initialization for platform devices, and then turn the dma_mask
into a scalar.