linux-kernel - Re: [RFC PATCH 1/2] common: dma-mapping: introduce dma_get_parent

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Message-ID: <549324B9.2030506@ti.com>
Date:	Thu, 18 Dec 2014 14:02:17 -0500
From:	Murali Karicheri <m-karicheri2@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arm-kernel@...ts.infradead.org>, <vinod.koul@...el.com>,
	<gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>,
	<dmaengine@...r.kernel.org>, <linux-pci@...r.kernel.org>,
	<bhelgaas@...gle.com>, <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>
Subject: Re: [RFC PATCH 1/2] common: dma-mapping: introduce dma_get_parent_cfg()
 helper

On 12/17/2014 07:09 PM, Arnd Bergmann wrote:
> On Wednesday 17 December 2014 18:24:43 Murali Karicheri wrote:
>> On 12/17/2014 04:56 PM, Arnd Bergmann wrote:
>>> On Wednesday 17 December 2014 13:02:23 Murali Karicheri wrote:
>>>
>>> What's wrong with using arch_setup_dma_ops() from PCI as suggested
>>> previously?
>>>
>
> +Will Deacon
>
>> I had originally written a code based on that line as below. But
>> dma-ranges property is also used by ppc and other architectures in the
>> pci device DT node. So I wasn't sure how this code impact PCI driver
>> functionality on those platforms. Hence used a simpler change as all
>> that is needed for keystone is to get the dma_pfn_offset rightly set in
>> the pci slave device.
>
> But in your patch, you don't call arch_setup_dma_ops() at all.
>
>> Initially I had a function implemented as below for this in of_pci.c.
>>
>> + * of_pci_dma_configure - Setup DMA configuration for a pci device
>> + * @dev:       pci device to apply DMA configuration
>> + *
>> + * Try to get devices's DMA configuration from DT and update it
>> + * accordingly. This is a similar to of_dma_configure() for platform
>> + * devices.
>> + *
>> + */
>> +void of_pci_dma_configure(struct pci_dev *dev)
>> +{
>> +       struct device *host_bridge, *parent;
>> +       struct pci_bus *bus = dev->bus;
>> +       u64 dma_addr, paddr, size;
>> +       int ret;
>> +
>> +       while (!pci_is_root_bus(bus))
>> +               bus = bus->parent;
>> +       host_bridge = bus->bridge;
>> +
>> +       parent = host_bridge->parent;
>> +       if (parent->of_node) {
>
> so far it looks good, although we may want to introduce
> a helper function to get the of_node.

Will add

>
>> +               /*
>> +                * if dma-coherent property exist, call arch hook to setup
>> +                * dma coherent operations.
>> +                */
>> +               if (of_dma_is_coherent(parent->of_node)) {
>> +                       set_arch_dma_coherent_ops(&dev->dev);
>> +                       dev_info(&dev->dev, "device is dma coherent\n");
>> +               }
>
> set_arch_dma_coherent_ops no longer exists. Just keep the flag in a
> local variable

Ok.

>
>> +               /*
>> +                * if dma-ranges property doesn't exist - just return else
>> +                * setup the dma offset
>> +                */
>> +               ret = of_dma_get_range(parent->of_node,&dma_addr,
>> &paddr,&size);
>> +               if (ret<  0) {
>> +                       dev_info(&dev->dev, "no dma range information to
>> setup\n");
>> +                       printk("no dma range information to setup\n");
>> +                       return;
>> +               }
>> +
>> +               /* DMA ranges found. Calculate and set dma_pfn_offset */
>> +               dev->dev.dma_pfn_offset = PFN_DOWN(paddr - dma_addr);
>> +               dev_info(&dev->dev, "dma_pfn_offset(%#08lx)\n",
>> dev->dev.dma_pfn_offset);
>
> Same for the offset and size here, then pass all of the above into
> arch_setup_dma_ops. This is also where we need to hook up the iommu
> support once we decide how to make that work with the ARM SMMU.

Ok. I will make this similar to of_dma_configure() that can be called 
from pci/probe.c

Murali
>
> Will, I think we may have a problem on ARM64 now, since we only replaced
> set_arch_dma_coherent_ops on ARM32 but not ARM64. Can you send a fix for
> this? Without that, we don't have any coherent operations on ARM64 any
> more, unless I'm missing something.
>
> 	Arnd
> --
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-- 
Murali Karicheri
Linux Kernel, Texas Instruments
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