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

[Stefan Wahren]

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?
> > >
> > > _______________________________________________
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> > > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
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