Re: [GIT PULL] i.MX fixes for 4.19, round 2

From: Lucas Stach <l.stach@pengutronix.de>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Sricharan R <sricharan@codeaurora.org>, arm-soc <arm@kernel.org>,
	linux-imx@nxp.com, Sascha Hauer <kernel@pengutronix.de>,
	Fabio Estevam <fabio.estevam@nxp.com>,
	Shawn Guo <shawnguo@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [GIT PULL] i.MX fixes for 4.19, round 2
Date: Mon, 17 Dec 2018 17:42:07 +0100	[thread overview]
Message-ID: <1545064927.5874.18.camel@pengutronix.de> (raw)
In-Reply-To: <CAK8P3a0d3C3gDi_Ozh1gBTVXiAOc67_8SOYh7tzWVpP8trO8-A@mail.gmail.com>

Hi Arnd,

Am Dienstag, den 02.10.2018, 14:09 +0200 schrieb Arnd Bergmann:
> On Tue, Oct 2, 2018 at 1:42 PM Lucas Stach <l.stach@pengutronix.de>
> wrote:
> > Am Dienstag, den 02.10.2018, 11:59 +0200 schrieb Arnd Bergmann:
> > > On Mon, Oct 1, 2018 at 4:39 AM Shawn Guo <shawnguo@kernel.org>
> > > wrote:
> > > > 
> > > > The following changes since commit
> > > > 57361846b52bc686112da6ca5368d11210796804:
> > > > 
> > > >   Linux 4.19-rc2 (2018-09-02 14:37:30 -0700)
> > > > 
> > > > are available in the git repository at:
> > > > 
> > > >  
> > > > git://git.kernel.org/pub/scm/linux/kernel/git/shawnguo/linux.gi
> > > > t
> > > > tags/imx-fixes-4.19-2
> > > > 
> > > > for you to fetch changes up to
> > > > 4d8d4712e47c028306149bda04b79f70325aefb0:
> > > > 
> > > >   soc: imx: gpc: set DMA mask for PD platform devices (2018-09-
> > > > 26
> > > > 10:38:38 +0800)
> > > > 
> > > > -------------------------------------------------------------
> > > > ---
> > > > i.MX fixes for 4.19, round 2:
> > > >  - There appears an uninitialized DMA mask warning on i.MX GPC
> > > > driver
> > > >    with 4.19-rc kernel.  Set the DMA mask for powerdomain
> > > > platform
> > > >    device to fix the warning given by device core.
> > > 
> > > I don't think this is the right fix, we should generally not just
> > > make up a dma
> > > mask pointer.
> > > 
> > > Lucas, do you have any more information regarding that warning?
> > > Are we trying to do DMA on a virtual device? What operation
> > > causes that warning?
> > 
> > The warning we are silencing here is generated by
> > of_dma_configure() if
> > the dma_mask is not set, which gets called for all devices with a
> > OF
> > node, regardless if the device is actually DMA capable.
> > As the platform bus code calls this function with force_dma = true,
> > the
> > absent dma-ranges won't stop this function from trying to set up
> > the
> > dma stuff, so I don't really see another clean way to get rid of
> > this
> > warning.
> 
> Ok, I see. So I think the warning is wrong here, and your change
> actually makes it worse, because we really /don't/ want to do DMA
> on this node.
> 
> From what I can tell, the change that introduced this behavior
> was commit 09515ef5ddad ("of/acpi: Configure dma operations at
> probe time for platform/amba/pci bus devices") in 4.12.
> 
> Before that, we did not try to call of_dma_configure() on a manually
> added device, which I think was the correct behavior. Does that
> correspond to what you are seeing?
> 
> For the moment, I'd prefer to hold off on this patch, until we have
> resolved what the best fix is going to be. Since there is no DMA
> on the device, the behavior will be correct, aside from the
> annoying warning.

Do you have an idea how to better fix this? The warning is annoying
(especially for people that aren't aware that this device doesn't need
any DMA setup).

I don't really see how we could fix this without regressing
functionality for other drivers. Thoughts?

Regards,
Lucas

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