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

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Date:   Tue, 24 Jan 2023 10:26:40 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Umang Jain <umang.jain@...asonboard.com>
Cc:     Stefan Wahren <stefan.wahren@...e.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,
        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 Umang,

On Tue, Jan 24, 2023 at 11:09:31AM +0530, Umang Jain wrote:
> On 1/23/23 10:58 PM, Stefan Wahren wrote:
> > Am 23.01.23 um 08:48 schrieb Umang Jain:
> >> On 1/23/23 5:04 AM, Stefan Wahren wrote:
> >>> 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 ?

Why shouldn't we ? :-)

> >> 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?

-- 
Regards,

Laurent Pinchart