linux-kernel - Re: [PATCH v6 0/6] staging: vc04_services: vchiq: Register devices with a custom bus

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Date:   Thu, 26 Jan 2023 19:03:16 +0530
From:   Umang Jain <umang.jain@...asonboard.com>
To:     Phil Elwell <phil@...pberrypi.com>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     linux-staging@...ts.linux.dev,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Adrien Thierry <athierry@...hat.com>,
        Dan Carpenter <error27@...il.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Paul Elder <paul.elder@...asonboard.com>
Subject: Re: [PATCH v6 0/6] staging: vc04_services: vchiq: Register devices
 with a custom bus_type

Hi Phil,

Thank you for the response

On 1/25/23 1:17 AM, Phil Elwell wrote:
> On 24/01/2023 8:41, Stefan Wahren wrote:
>> Hi Phil,
>>
>> Am 23.01.23 um 09:58 schrieb Laurent Pinchart:
>>> On Mon, Jan 23, 2023 at 01:18:30PM +0530, Umang Jain wrote:
>>>> Hi Stefan,
>>>>
>>>> Thank for the testing.
>>>>
>>>> On 1/23/23 5:04 AM, Stefan Wahren wrote:
>>>>> Hi Umang,
>>>>>
>>>>> Am 20.01.23 um 21:10 schrieb Umang Jain:
>>>>>> This series just introduces five extra patches for dropping include
>>>>>> directives from Makefiles (suggested by Greg KH) and rebased.
>>>>>>
>>>>>> The main patch (6/6) removes platform device/driver abuse and moves
>>>>>> things to standard device/driver model using a custom_bus. Specific
>>>>>> details are elaborated in the commit message.
>>>>>>
>>>>>> The patch series is based on top of d514392f17fd (tag: 
>>>>>> next-20230120)
>>>>>> of linux-next.
>>>>> applied this series on top of linux-next and build it with
>>>>> arm/multi_v7_defconfig plus the following:
>>>>>
>>>>> CONFIG_BCM_VIDEOCORE=y
>>>>> CONFIG_BCM2835_VCHIQ=m
>>>>> CONFIG_VCHIQ_CDEV=y
>>>>> CONFIG_SND_BCM2835=m
>>>>> CONFIG_VIDEO_BCM2835=m
>>>>> CONFIG_BCM2835_VCHIQ_MMAL=m
>>>>>
>>>>> and the devices doesn't register on Raspberry Pi 3 B Plus:
>>>>>
>>>>> [   25.523337] vchiq: module is from the staging directory, the 
>>>>> quality is unknown, you have been warned.
>>>>> [   25.541647] bcm2835_vchiq 3f00b840.mailbox: Failed to register 
>>>>> bcm2835_audio vchiq device
>>>>> [   25.553692] bcm2835_vchiq 3f00b840.mailbox: Failed to register 
>>>>> bcm2835-camera vchiq device
>>>> I was able to reproduce and it seems the issue here is the change
>>>> mentioned in the cover
>>>>
>>>> - drop dma_set_mask_and_coherent
>>>>
>>>> in V6.
>>>>
>>>> (I usually test patches on RPi 4B with vcsm-cma and bcm2835-isp 
>>>> applied
>>>> so my branch has the DMA hunk included while I was testing V6)
>>>>
>>>> Below is the hunk which should resolve the issue.
>>>>
>>>> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_device.c
>>>> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_device.c
>>>> @@ -6,6 +6,7 @@
>>>>     */
>>>>
>>>>    #include <linux/device/bus.h>
>>>> +#include <linux/dma-mapping.h>
>>>>    #include <linux/slab.h>
>>>>    #include <linux/string.h>
>>>>
>>>> @@ -72,6 +73,12 @@ int vchiq_device_register(struct device *parent,
>>>> const char *name)
>>>>           device->dev.type = &vchiq_device_type;
>>>>           device->dev.release = vchiq_device_release;
>>>>
>>>> +       ret = dma_set_mask_and_coherent(&device->dev, 
>>>> DMA_BIT_MASK(32));
>>>> +       if (ret < 0) {
>>>> +               vchiq_device_release(&device->dev);
>>>> +               return ret;
>>>> +       }
>>>> +
>>>>           ret = device_register(&device->dev);
>>>>           if (ret) {
>>>>                   put_device(&device->dev);
>>>>
>>>> It seems we need to include the dma_set_mask_and_coherent() even if
>>>> bcm2835-audio, bcm2835-camera device doesn't do DMA? I need to look 
>>>> into
>>>> why is that/
>>
>> Do you have an answer for this?
>
> That's because vchiq does use DMA for bulk transfers, it's just that 
> the DMA hardware
> is driven from the VPU side. And even though the VPU can only address 
> 1GB, it uses the
> upper address bits to determine cacheability of accesses, hence the 
> need for 32-bit
> DMA addresses.

Is it worth recording this as a comment  in the patch?
>
> Phil
>