linux-kernel - Re: [PATCH] ARM: keystone: add bus notifier to set dma_pfn

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Date:	Fri, 10 Oct 2014 17:37:11 -0400
From:	Murali Karicheri <m-karicheri2@...com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arm-kernel@...ts.infradead.org>, <linux@....linux.org.uk>,
	<linux-kernel@...r.kernel.org>, <santosh.shilimkar@...com>
Subject: Re: [PATCH] ARM: keystone: add bus notifier to set dma_pfn_offset
 for pci devices

On 10/10/2014 02:22 PM, Arnd Bergmann wrote:
> On Friday 10 October 2014 11:15:37 Murali Karicheri wrote:
>> @@ -54,6 +55,8 @@ static void __init keystone_init(void)
>>          keystone_pm_runtime_init();
>>          if (platform_nb.notifier_call)
>>                  bus_register_notifier(&platform_bus_type,&platform_nb);
>> +       if (platform_nb.notifier_call)
>> +               bus_register_notifier(&pci_bus_type,&platform_nb);
>>          of_platform_populate(NULL, of_default_bus_match_table, NULL, NULL);
>>
>
> No, this looks very wrong. Santosh spent an enormous effort on obsoleting
> the platform notifier block by adding the range parser to the platform
> device probe path.
>
> You should really remove platform_nb and all associated code rather than
> adding more code to it.
>
> NAK
>
> 	Arnd
Arnd,

I took a look at the recent work from Santosh where he has introduced 
dma-range property to set the dma_pfn_offset for platform devices. Are 
you referring to this commit below?

commit 591c1ee465ce5372385dbc41e7d3e36cbb477bd8
Author: Santosh Shilimkar <santosh.shilimkar@...com>
Date:   Thu Apr 24 11:30:04 2014 -0400

     of: configure the platform device dma parameters

     Retrieve DMA configuration from DT and setup platform device's DMA
     parameters. The DMA configuration in DT has to be specified using
     "dma-ranges" and "dma-coherent" properties if supported.

     We setup dma_pfn_offset using "dma-ranges" and dma_coherent_ops
     using "dma-coherent" device tree properties.

     The set_arch_dma_coherent_ops macro has to be defined by arch if
     it supports coherent dma_ops. Otherwise, set_arch_dma_coherent_ops() is
     declared as nop.

Based on this, dma configuration parameters get set for the device which 
is probed through DT.

As PCI devices are attached to the PCI bus during scan, and we don't 
have DT nodes, we could use similar mechanism to pass the dma-range info 
from parent host platform device to the PCI devices by adding an 
of_pci_dma_configure() API and hook it to the PCI probe path some where?
Please comment on this so that I can work on the right solution to 
address this issue for Keystone.

-- 
Murali Karicheri
Linux Kernel, Texas Instruments
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