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

[Umang Jain]

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