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From: Finn Thain <fthain@telegraphics.com.au>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "David S. Miller" <davem@davemloft.net>,
	linux-m68k <linux-m68k@vger.kernel.org>,
	netdev <netdev@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH net] macmace: Set platform device coherent_dma_mask
Date: Thu, 10 May 2018 11:25:35 +1000 (AEST)	[thread overview]
Message-ID: <alpine.LNX.2.21.1805091805130.72@nippy.intranet> (raw)
In-Reply-To: <CAMuHMdU1XBqt7hwEW6JTas64ZNGCGCMr5HMZwuLo0O-ZBCOWyA@mail.gmail.com>

On Thu, 3 May 2018, Geert Uytterhoeven wrote:

> 
> Perhaps you can add a new helper 
> (platform_device_register_simple_dma()?) that takes the DMA mask, too?

Would there be enough potential callers in future to justify that API?
It seems that there haven't been many in the past. I found four users of 
platform_device_register_simple() which might benefit. Mostly these call 
dma_set_coherent_mask() in the platform driver probe routine.

drivers/gpu/drm/etnaviv/etnaviv_drv.c
drivers/gpu/drm/exynos/exynos_drm_drv.c
drivers/gpu/drm/omapdrm/omap_drv.c
drivers/parport/parport_pc.c

(Am I missing any others?)

To actually hoist the dma mask setup out of existing platform drivers 
would have implications for every device that matches with those drivers. 

That's a bit risky since I can't test those devices -- that's assuming I 
could identify them all; sometimes platform device matching is not well 
defined at build time (see loongson_sysconf.ecname).

So far, it looks like macmace and macsonic would be the only callers of 
this new API call.

What's worse, if you do pass a dma_mask in struct platform_device_info, 
you end up with this problem in platform_device_register_full():

        if (pdevinfo->dma_mask) {
                /*
                 * This memory isn't freed when the device is put,
                 * I don't have a nice idea for that though.  Conceptually
                 * dma_mask in struct device should not be a pointer.
                 * See http://thread.gmane.org/gmane.linux.kernel.pci/9081
                 */
                pdev->dev.dma_mask =
                        kmalloc(sizeof(*pdev->dev.dma_mask), GFP_KERNEL);

Most of the platform drivers that call dma_coerce_mask_and_coherent() are 
using pdev->of_match_table, not platform_device_register_simple(). Many of 
them have a comment like this:

        /*
         * Right now device-tree probed devices don't get dma_mask set.
         * Since shared usb code relies on it, set it here for now.
         * Once we have dma capability bindings this can go away.
         */

> With people setting the mask to kill the WARNING splat, this may become 
> more common.

Since the commit which introduced the WARNING, only commits f61e64310b75 
("m68k: set dma and coherent masks for platform FEC ethernets") and 
7bcfab202ca7 ("powerpc/macio: set a proper dma_coherent_mask") seem to be 
aimed at squelching that WARNING.

(Am I missing any others?)

So far, this is not looking like a common problem, and I'm having trouble 
finding some way to improve on my original patches.

-- 

  parent reply	other threads:[~2018-05-10  1:25 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <S1751632AbeECEYA/20180503042400Z+254@vger.kernel.org>
2018-05-03  7:25 ` Geert Uytterhoeven
2018-05-03  8:38   ` Finn Thain
2018-05-03  8:46     ` Geert Uytterhoeven
2018-05-03  8:51       ` Christoph Hellwig
2018-05-03 20:24         ` Michael Schmitz
2018-05-04  7:24           ` Geert Uytterhoeven
2018-05-04  8:16             ` Michael Schmitz
2018-05-10  1:25         ` Finn Thain
2018-05-10  1:25       ` Finn Thain [this message]
2018-05-10 20:27         ` Michael Schmitz
2018-05-10 23:55           ` Finn Thain
2018-05-11  2:11             ` Michael Schmitz
2018-05-11  3:28               ` Finn Thain
2018-05-11  4:18                 ` Michael Schmitz
2018-05-11  5:28                   ` Finn Thain
2018-05-11  9:30                     ` Michael Schmitz
2018-05-11 10:06                       ` Finn Thain
2018-05-11 22:02                         ` Michael Schmitz
2018-05-03  4:23 Finn Thain

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