From: Felipe Balbi <balbi@kernel.org>
To: Arnd Bergmann <arnd@arndb.de>, linux-arm-kernel@lists.infradead.org
Cc: Grygorii Strashko <grygorii.strashko@ti.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
linux-usb@vger.kernel.org, Sekhar Nori <nsekhar@ti.com>,
linux-kernel@vger.kernel.org,
David Fisher <david.fisher1@synopsys.com>,
"Thang Q. Nguyen" <tqnguyen@apm.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev
Date: Wed, 27 Apr 2016 23:57:17 +0300 [thread overview]
Message-ID: <87zisercr6.fsf@ti.com> (raw)
In-Reply-To: <6148633.0YXW4XnX4b@wuerfel>
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Hi,
Arnd Bergmann <arnd@arndb.de> writes:
> On Wednesday 27 April 2016 19:53:51 Felipe Balbi wrote:
>> Arnd Bergmann <arnd@arndb.de> writes:
>> > On Wednesday 27 April 2016 16:50:19 Catalin Marinas wrote:
>> >> On Wed, Apr 27, 2016 at 04:11:17PM +0200, Arnd Bergmann wrote:
>> >> > On Wednesday 27 April 2016 14:59:00 Catalin Marinas wrote:
>> >> > >
>> >> > > I would be in favour of a dma_inherit() function as well. We could hack
>> >> > > something up in the arch code (like below) but I would rather prefer an
>> >> > > explicit dma_inherit() call by drivers creating such devices.
>> >> > >
>> >> > > diff --git a/arch/arm64/include/asm/dma-mapping.h b/arch/arm64/include/asm/dma-mapping.h
>> >> > > index ba437f090a74..ea6fb9b0e8fa 100644
>> >> > > --- a/arch/arm64/include/asm/dma-mapping.h
>> >> > > +++ b/arch/arm64/include/asm/dma-mapping.h
>> >> > > @@ -29,8 +29,11 @@ extern struct dma_map_ops dummy_dma_ops;
>> >> > >
>> >> > > static inline struct dma_map_ops *__generic_dma_ops(struct device *dev)
>> >> > > {
>> >> > > - if (dev && dev->archdata.dma_ops)
>> >> > > - return dev->archdata.dma_ops;
>> >> > > + while (dev) {
>> >> > > + if (dev->archdata.dma_ops)
>> >> > > + return dev->archdata.dma_ops;
>> >> > > + dev = dev->parent;
>> >> > > + }
>> >> >
>> >> > I think this would be a very bad idea: we don't want to have random
>> >> > devices be able to perform DMA just because their parent devices
>> >> > have been set up that way.
>> >>
>> >> I agree, it's a big hack. It would be nice to have a simpler way to do
>> >> this in driver code rather than explicitly calling
>> >> of_dma_configure/arch_setup_dma_ops as per the original patch in this
>> >> thread.
>> >
>> > I haven't followed the entire discussion, but what's wrong with passing
>> > around a pointer to a 'struct device *hwdev' that represents the physical
>> > device that does the DMA?
>>
>> that will likely create duplicated solutions in several drivers and
>> it'll be a pain to maintain. There's another complication, dwc3 can be
>> integrated in many different ways. See the device child-parent tree
>> representations below:
>>
>> a) with a parent PCI device:
>>
>> pci_bus_type
>> - dwc3-pci
>> - dwc3
>> - xhci-plat
>>
>> b) with a parent platform_device (OF):
>>
>> platform_bus_type
>> - dwc3-${omap,st,of-simple,exynos,keystone}
>> - dwc3
>> - xhci-plat
>>
>> c) without a parent at all (thanks Grygorii):
>>
>> platform_bus_type
>> - dwc3
>> - xhci-plat
>>
>> (a) and (b) above are the common cases. The DMA-capable device is
>> clearly dwc3-${pci,omap,st,of-simple,exynos,keystone} with dwc3 only
>> having proper DMA configuration in OF platforms (because of the
>> unconditional of_dma_configure() during OF device creation) and
>> xhci-plat not knowing about DMA at all and hardcoding some crappy
>> defaults.
>>
>> (c) is the uncommon case which creates some problems. In this case, dwc3
>> itself is the DMA-capable device and dwc3->dev->parent is the
>> platform_bus_type itself. Now consider the problem this creates:
>>
>> i. the patch that I wrote [1] becomes invalid for (c), thanks to
>> Grygorii for pointing this out before it was too late.
>>
>> ii. xhci-plat can also be described directly in DT (and is in some
>> cases). This means that assuming xhci-plat's parent's parent to be the
>> DMA-capable device is also an invalid assumption.
>>
>> iii. one might argue that for DT-based platforms *with* a glue layer
>> ((b) above), OF already "copies" some sensible DMA defaults during
>> device creation.
>
> But that is exactly the point I was trying to make: instead of copying
> all the data into the xhci-plat device, just assign one pointer
> inside the xhci-plat device from whoever creates it.
and how do you pass that pointer to xhci-plat from another driver ?
No, platform_data is not an option ;-)
>> The only clean way to fix this up is with a dma_inherit()-like API which
>> would allow dwc3's glue layers ((a) and (b) above) to initialize child's
>> (dwc3) DMA configuration during child's creation. Something like below:
>>
>> diff --git a/drivers/usb/dwc3/dwc3-pci.c b/drivers/usb/dwc3/dwc3-pci.c
>> index adc1e8a624cb..74b599269e2c 100644
>> --- a/drivers/usb/dwc3/dwc3-pci.c
>> +++ b/drivers/usb/dwc3/dwc3-pci.c
>> @@ -152,6 +152,8 @@ static int dwc3_pci_probe(struct pci_dev *pci,
>> return -ENOMEM;
>> }
>>
>> + dma_inherit(&dwc->dev, dev);
>> +
>> memset(res, 0x00, sizeof(struct resource) * ARRAY_SIZE(res));
>>
>> res[0].start = pci_resource_start(pci, 0);
>>
>> that's all I'm asking for :-) dma_inherit() should, probably, be
>> arch-specific to handle details like IOMMU (which today sits under
>> archdata).
>
> It's still wrong: the archdata in the device can contain all sorts of
> additional information about how to do DMA, and some of that information
yes, inherit all of that ;-)
> is bus specific, e.g. when your dma_map_ops look like the on sparc:
okay, let me be clear. The underlying bus is still pci_bus_type or
platform_bus_type; that won't change.
> static inline struct dma_map_ops *get_dma_ops(struct device *dev)
> {
> #ifdef CONFIG_SPARC_LEON
> if (sparc_cpu_model == sparc_leon)
> return leon_dma_ops;
> #endif
> #if defined(CONFIG_SPARC32) && defined(CONFIG_PCI)
> if (dev->bus == &pci_bus_type)
> return &pci32_dma_ops;
> #endif
> return dma_ops;
> }
this seems to be a rather fragile assumption, no ? Only works because
*_bus_type declarations are exported. I wonder if this is the only
reason *why* they are exported, probably not...
> There is no way for a device to "inherit" the bus_type of its parent,
I don't want to inherit bus_type, I just want DMA configuration to not
depend on bus_type directly ;-)
--
balbi
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next prev parent reply other threads:[~2016-04-27 20:57 UTC|newest]
Thread overview: 91+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-25 19:21 [PATCH] usb: dwc3: host: inherit dma configuration from parent dev Grygorii Strashko
2016-04-26 6:17 ` Felipe Balbi
2016-04-26 8:14 ` Grygorii Strashko
2016-04-27 5:41 ` Felipe Balbi
2016-04-27 11:55 ` Grygorii Strashko
2016-04-27 13:59 ` Catalin Marinas
2016-04-27 14:11 ` Arnd Bergmann
2016-04-27 15:50 ` Catalin Marinas
2016-04-27 16:04 ` Arnd Bergmann
2016-04-27 16:53 ` Felipe Balbi
2016-04-27 17:42 ` Arnd Bergmann
2016-04-27 17:59 ` Alan Stern
2016-04-27 18:08 ` Arnd Bergmann
2016-04-27 20:05 ` Felipe Balbi
2016-04-27 21:05 ` Arnd Bergmann
2016-04-28 6:37 ` Felipe Balbi
2016-04-28 14:16 ` Russell King - ARM Linux
2016-04-28 14:23 ` Arnd Bergmann
2016-04-28 14:27 ` Felipe Balbi
2016-09-01 22:14 ` Leo Li
2016-09-02 10:43 ` Arnd Bergmann
2016-09-02 10:47 ` Russell King - ARM Linux
2016-09-02 11:08 ` Felipe Balbi
2016-09-02 14:11 ` Felipe Balbi
2016-09-02 14:21 ` Alan Stern
2016-09-02 15:51 ` Arnd Bergmann
2016-09-07 7:17 ` Roger Quadros
2016-09-07 8:29 ` Arnd Bergmann
2016-09-07 13:04 ` Roger Quadros
2016-09-07 14:38 ` Arnd Bergmann
2016-09-02 16:23 ` Grygorii Strashko
2016-09-02 10:53 ` Felipe Balbi
2016-09-02 11:55 ` Robin Murphy
2016-09-02 12:56 ` Felipe Balbi
2016-09-02 13:10 ` Arnd Bergmann
2016-09-02 22:16 ` Leo Li
2016-09-05 15:39 ` Arnd Bergmann
2016-09-06 6:35 ` Peter Chen
2016-09-06 6:40 ` Felipe Balbi
2016-09-06 10:46 ` Arnd Bergmann
2016-09-06 10:50 ` Felipe Balbi
2016-09-06 13:27 ` Arnd Bergmann
2016-09-07 6:51 ` Felipe Balbi
2016-09-07 7:44 ` Peter Chen
2016-09-07 8:52 ` Arnd Bergmann
2016-09-07 9:29 ` Peter Chen
2016-09-07 9:35 ` Russell King - ARM Linux
2016-09-07 10:18 ` Felipe Balbi
2016-09-06 10:38 ` Arnd Bergmann
2016-09-07 6:33 ` Peter Chen
2016-09-07 8:48 ` Arnd Bergmann
2016-09-07 9:55 ` Peter Chen
2016-09-07 10:33 ` Robin Murphy
2016-09-07 10:47 ` Felipe Balbi
2016-09-14 16:31 ` Lorenzo Pieralisi
2016-09-14 21:50 ` Arnd Bergmann
2016-09-07 10:24 ` Felipe Balbi
2016-09-07 15:24 ` Arnd Bergmann
2016-09-07 16:08 ` Alan Stern
2016-09-07 19:45 ` Arnd Bergmann
2016-09-08 1:15 ` Peter Chen
2016-09-08 8:02 ` Arnd Bergmann
2016-09-08 8:03 ` Felipe Balbi
2016-09-08 8:26 ` Arnd Bergmann
2016-09-08 8:29 ` Felipe Balbi
2016-09-08 8:45 ` Arnd Bergmann
2016-09-08 9:43 ` Felipe Balbi
2016-09-08 10:17 ` Arnd Bergmann
2016-09-08 11:00 ` Felipe Balbi
2016-09-08 11:11 ` Arnd Bergmann
2016-09-08 11:20 ` Felipe Balbi
2016-09-08 11:39 ` Arnd Bergmann
2016-09-08 11:52 ` Felipe Balbi
2016-09-08 12:46 ` Arnd Bergmann
2016-09-08 12:02 ` Grygorii Strashko
2016-09-08 12:14 ` Arnd Bergmann
2016-09-08 12:28 ` Peter Chen
2016-09-08 12:52 ` Arnd Bergmann
2016-09-09 1:37 ` Peter Chen
2016-09-08 12:59 ` Grygorii Strashko
2016-09-09 1:52 ` Peter Chen
2016-09-21 11:06 ` Sriram Dash
2016-09-21 11:31 ` Arnd Bergmann
2016-09-21 11:43 ` Sriram Dash
2016-09-21 12:48 ` Arnd Bergmann
2016-09-22 5:02 ` Sriram Dash
2016-10-07 22:46 ` Leo Li
2016-09-21 17:14 ` [PATCH] usb: xhci: Fix the patch inherit dma configuration from kbuild test robot
2016-04-27 20:57 ` Felipe Balbi [this message]
2016-04-27 14:14 ` [PATCH] usb: dwc3: host: inherit dma configuration from parent dev Grygorii Strashko
2016-05-05 17:07 ` Brian Norris
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