linux-kernel - Re: [PATCHv4 06/14] remoteproc/omap: Initialize and assign reserved memory node

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Date:   Tue, 7 Jan 2020 16:25:12 +0200
From:   Tero Kristo <t-kristo@...com>
To:     "Andrew F. Davis" <afd@...com>, <bjorn.andersson@...aro.org>,
        <ohad@...ery.com>, <linux-remoteproc@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <mathieu.poirier@...aro.org>,
        <linux-omap@...r.kernel.org>, <s-anna@...com>
Subject: Re: [PATCHv4 06/14] remoteproc/omap: Initialize and assign reserved
 memory node

On 07/01/2020 15:37, Andrew F. Davis wrote:
> On 1/2/20 8:18 AM, Tero Kristo wrote:
>> From: Suman Anna <s-anna@...com>
>>
>> The reserved memory nodes are not assigned to platform devices by
>> default in the driver core to avoid the lookup for every platform
>> device and incur a penalty as the real users are expected to be
>> only a few devices.
>>
>> OMAP remoteproc devices fall into the above category and the OMAP
>> remoteproc driver _requires_ specific CMA pools to be assigned
>> for each device at the moment to align on the location of the
>> vrings and vring buffers in the RTOS-side firmware images. So,
> 
> 
> Requires only at the moment due to firmware..
> 
> This sounds like some firmware images hard-coded their vring addresses
> instead of getting them dynamically as they should and we are hacking
> around that on the kernel side by giving them the addresses they use as
> carveouts.

The firmwares are built on specific device addresses, this includes data 
+ code.

> Should we rather make use of the IOMMU attached to the DSP to map any
> kernel address to the DSP where the firmware expects it? Or better yet
> fixup the firmwares.

Well, we do use IOMMU to map the corresponding memory area to specific 
device address. What this patch does, is to allocate a contiguous memory 
area for the remoteproc shared memories. Using completely random memory 
location would potentially fragment the remoteproc memory around page 
boundaries, resulting in a complex (read ineffective) IOMMU mapping. 
Also, we are going to need the reserved memory mechanism for the 
remoteproc anyways later, as we are going to introduce the support for 
early-boot / late-attach. Bootloader would pass the used memory regions 
to the kernel via the reserved memory nodes in that case (unless we 
assume to use some hardcoded region, which would be worse than passing 
it via DT.)

-Tero

> 
> DRAM carveouts should be a last resort used only for when hardware
> really requires it.
> 
> Andrew
> 
> 
>> use the of_reserved_mem_device_init/release() API appropriately
>> to assign the corresponding reserved memory region to the OMAP
>> remoteproc device. Note that only one region per device is
>> allowed by the framework.
>>
>> Signed-off-by: Suman Anna <s-anna@...com>
>> Signed-off-by: Tero Kristo <t-kristo@...com>
>> Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>> ---
>>   drivers/remoteproc/omap_remoteproc.c | 12 +++++++++++-
>>   1 file changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/remoteproc/omap_remoteproc.c b/drivers/remoteproc/omap_remoteproc.c
>> index 9ca337f18ac2..8a6dd742a8b1 100644
>> --- a/drivers/remoteproc/omap_remoteproc.c
>> +++ b/drivers/remoteproc/omap_remoteproc.c
>> @@ -17,6 +17,7 @@
>>   #include <linux/module.h>
>>   #include <linux/err.h>
>>   #include <linux/of_device.h>
>> +#include <linux/of_reserved_mem.h>
>>   #include <linux/platform_device.h>
>>   #include <linux/dma-mapping.h>
>>   #include <linux/remoteproc.h>
>> @@ -480,14 +481,22 @@ static int omap_rproc_probe(struct platform_device *pdev)
>>   	if (ret)
>>   		goto free_rproc;
>>   
>> +	ret = of_reserved_mem_device_init(&pdev->dev);
>> +	if (ret) {
>> +		dev_err(&pdev->dev, "device does not have specific CMA pool\n");
>> +		goto free_rproc;
>> +	}
>> +
>>   	platform_set_drvdata(pdev, rproc);
>>   
>>   	ret = rproc_add(rproc);
>>   	if (ret)
>> -		goto free_rproc;
>> +		goto release_mem;
>>   
>>   	return 0;
>>   
>> +release_mem:
>> +	of_reserved_mem_device_release(&pdev->dev);
>>   free_rproc:
>>   	rproc_free(rproc);
>>   	return ret;
>> @@ -499,6 +508,7 @@ static int omap_rproc_remove(struct platform_device *pdev)
>>   
>>   	rproc_del(rproc);
>>   	rproc_free(rproc);
>> +	of_reserved_mem_device_release(&pdev->dev);
>>   
>>   	return 0;
>>   }
>>

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