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

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Message-ID: <86e02148-c258-3362-90f3-827e7654775e@i2se.com>
Date:   Tue, 24 Jan 2023 09:39:16 +0100
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Umang Jain <umang.jain@...asonboard.com>,
        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
Cc:     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>,
        Laurent Pinchart <laurent.pinchart@...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 Umang,

Am 24.01.23 um 06:39 schrieb Umang Jain:
> Hi Stefan
>
> On 1/23/23 10:58 PM, Stefan Wahren wrote:
>> Hi Umang,
>>
>> Am 23.01.23 um 08:48 schrieb Umang Jain:
>>> 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);
>> Yes, this patch fixes the errors above. But i noticed that the series 
>> also break autoprobing of bcm2835-audio and bcm2835-camera.
>
> For the diff concerned, I am still looking into why is this needed.
>
> Regarding the autoprobing, I have noticed that as well. It seems the 
> probing is automatic for platform driver/devices and we are moving 
> away from the platform driver/devices. So, this is expected I suppose?
>
> Reading from Documentation/driver-api/driver-model/platform.rst
>
> """
> Driver binding is performed automatically by the driver core, invoking 
> driver probe() after finding a match between device and driver. If the 
> probe() succeeds, the driver and device are bound as usual
> """
>
> Should we retain this behavior ?
 From user perspective this behavior change is a regression. So we need 
automatic probing to convince user to use the mainline kernel.
>>>
>>> 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/
>>>
>>>  Laurent, any thoughts on this please?
>>>
>>> _______________________________________________
>>> linux-arm-kernel mailing list
>>> linux-arm-kernel@...ts.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>

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