linux-kernel - Re: [RFC 2/2] drivers: dma-mapping: parse per device reserved mem at probe time

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Message-id: <e44416ee-0f33-e310-d881-aaa3edfdf69e@samsung.com>
Date:   Mon, 27 Nov 2017 09:44:20 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Peng Fan <van.freenix@...il.com>
Cc:     Peng Fan <peng.fan@....com>, hch@....de, robin.murphy@....com,
        gregkh@...uxfoundation.org, robh+dt@...nel.org,
        frowand.list@...il.com, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [RFC 2/2] drivers: dma-mapping: parse per device reserved mem
 at probe time

Hi Peng,

On 2017-11-27 09:37, Peng Fan wrote:
> Hi Marek,
>
> On Mon, Nov 27, 2017 at 09:31:00AM +0100, Marek Szyprowski wrote:
>> Hi
>>
>> On 2017-11-26 14:13, Peng Fan wrote:
>>> Invoke of_reserved_mem_device_init at dma_configure, then
>>> there is no need to call of_reserved_mem_device_init in device
>>> specific probe function.
>>>
>>> Signed-off-by: Peng Fan <peng.fan@....com>
>> This has been already tried long time ago, without success:
>> http://patches.linaro.org/patch/33558/
> Thanks for the info. I should first search mail list before
> sending out patches.

It doesn't mean that I'm against such idea. I just pointed that I've
already tried. That time, however there was no dma_configure() function
yet, which seems to be better place for of_rmem_device_init().

I would however always call of_dma_configure(), even when reserved mem
node is there. IIRC on ARM64 that function configures dma_ops, without
which no dma is possible at all.

>
> Thanks,
> Peng.
>
>>> ---
>>>    drivers/base/dma-mapping.c | 6 +++++-
>>>    1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
>>> index e584eddef0a7..55dca06a7b55 100644
>>> --- a/drivers/base/dma-mapping.c
>>> +++ b/drivers/base/dma-mapping.c
>>> @@ -12,6 +12,7 @@
>>>    #include <linux/export.h>
>>>    #include <linux/gfp.h>
>>>    #include <linux/of_device.h>
>>> +#include <linux/of_reserved_mem.h>
>>>    #include <linux/slab.h>
>>>    #include <linux/vmalloc.h>
>>> @@ -351,7 +352,9 @@ int dma_configure(struct device *dev)
>>>    	}
>>>    	if (dma_dev->of_node) {
>>> -		ret = of_dma_configure(dev, dma_dev->of_node);
>>> +		ret = of_reserved_mem_device_init(dev);
>>> +		if (ret)
>>> +			ret = of_dma_configure(dev, dma_dev->of_node);
>>>    	} else if (has_acpi_companion(dma_dev)) {
>>>    		attr = acpi_get_dma_attr(to_acpi_device_node(dma_dev->fwnode));
>>>    		if (attr != DEV_DMA_NOT_SUPPORTED)
>>> @@ -367,5 +370,6 @@ int dma_configure(struct device *dev)
>>>    void dma_deconfigure(struct device *dev)
>>>    {
>>>    	of_dma_deconfigure(dev);
>>> +	of_reserved_mem_device_release(dev);
>>>    	acpi_dma_deconfigure(dev);
>>>    }

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland