Date:   Thu, 30 Jan 2020 13:55:49 -0600
From:   Suman Anna <s-anna@...com>
To:     Tero Kristo <t-kristo@...com>, "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>
Subject: Re: [PATCHv5 06/14] remoteproc/omap: Initialize and assign reserved
 memory node

On 1/30/20 1:42 PM, Tero Kristo wrote:
> On 30/01/2020 21:20, Andrew F. Davis wrote:
>> On 1/30/20 2:18 PM, Tero Kristo wrote:
>>> On 30/01/2020 20:11, Andrew F. Davis wrote:
>>>> On 1/16/20 8:53 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,
>>>>
>>>>
>>>> Same comment as before, this is a firmware issue for only some
>>>> firmwares
>>>> that do not handle being assigned vring locations correctly and instead
>>>> hard-code them.

As for this statement, this can do with some updating. Post 4.20,
because of the lazy allocation scheme used for carveouts including the
vrings, the resource tables now have to use FW_RSC_ADDR_ANY and will
have to wait for the vdev synchronization to happen.

>>>
>>> I believe we discussed this topic in length in previous version but
>>> there was no conclusion on it.
>>>
>>> The commit desc might be a bit misleading, we are not actually forced to
>>> use specific CMA buffers, as we use IOMMU to map these to device
>>> addresses. For example IPU1/IPU2 use internally exact same memory
>>> addresses, iommu is used to map these to specific CMA buffer.
>>>
>>> CMA buffers are mostly used so that we get aligned large chunk of memory
>>> which can be mapped properly with the limited IOMMU OMAP family of chips
>>> have. Not sure if there is any sane way to get this done in any other
>>> manner.
>>>
>>
>>
>> Why not use the default CMA area?
> 
> I think using default CMA area getting the actual memory block is not
> guaranteed and might fail. There are other users for the memory, and it
> might get fragmented at the very late phase we are grabbing the memory
> (omap remoteproc driver probe time.) Some chunks we need are pretty large.
> 
> I believe I could experiment with this a bit though and see, or Suman
> could maybe provide feedback why this was designed initially like this
> and why this would not be a good idea.

I have given some explanation on this on v4 as well, but if it is not
clear, there are restrictions with using default CMA. Default CMA has
switched to be assigned from the top of the memory (higher addresses,
since 3.18 IIRC), and the MMUs on IPUs and DSPs can only address
32-bits. So, we cannot blindly use the default CMA pool, and this will
definitely not work on boards > 2 GB RAM. And, if you want to add in any
firewall capability, then specific physical addresses becomes mandatory.

regards
Suman

> 
> -Tero
> 
>>
>> Andrew
>>
>>
>>> -Tero
>>>
>>>>
>>>> This is not a requirement of the remote processor itself and so it
>>>> should not fail to probe if a specific memory carveout isn't given.
>>>>
>>>>
>>>>> 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>
>>>>> ---
>>>>> v5: no changes
>>>>>
>>>>>    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 0846839b2c97..194303b860b2 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;
>>>>>    }
>>>>>
>>>
>>> -- 
> 
> -- 
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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