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.
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