Messages in this thread | | | Date | Thu, 22 Dec 2022 13:59:28 +0530 | Subject | Re: [PATCH] staging: vc04_services: vchiq_arm: Create platform_device per device | From | Umang Jain <> |
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Hi Greg, Laurent
thank you for the feedback
On 12/21/22 6:40 PM, Greg Kroah-Hartman wrote: > On Wed, Dec 21, 2022 at 01:14:59PM +0200, Laurent Pinchart wrote: >> Hi Umang, >> >> Thank you for the patch. >> >> On Tue, Dec 20, 2022 at 02:14:04PM +0530, Umang Jain wrote: >>> Create a proper per device platorm_device structure for all the child >>> devices that needs to be registered by vchiq platform driver. Replace >>> the vchiq_register_child() with platform_add_devices() to register the >>> child devices. >> This explains what the patch does, but not why. >> >>> This is part of an effort to address TODO item "Get rid of all non >>> essential global structures and create a proper per device structure" >> And this explains part of the reason only. Could you please expand the >> commit message with the reasoning behind this change ? It's not clear >> from the change below why this is needed and good.
Ok, I thought the TODO reference was sufficient but I'll expand on it. >> >>> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com> >>> --- >>> .../interface/vchiq_arm/vchiq_arm.c | 59 ++++++++++--------- >>> 1 file changed, 31 insertions(+), 28 deletions(-) >>> >>> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c >>> index 22de23f3af02..fa42ea3791a7 100644 >>> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c >>> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c >>> @@ -65,8 +65,29 @@ int vchiq_susp_log_level = VCHIQ_LOG_ERROR; >>> DEFINE_SPINLOCK(msg_queue_spinlock); >>> struct vchiq_state g_state; >>> >>> -static struct platform_device *bcm2835_camera; >>> -static struct platform_device *bcm2835_audio; >>> +static u64 vchiq_device_dmamask = DMA_BIT_MASK(32); >> The fact that this isn't const and is used by two different >> platform_device instances is worrying. Either it can be made const, or >> it's wrong.
ack. >> >>> + >>> +static struct platform_device bcm2835_camera = { >>> + .name = "bcm2835-camera", >>> + .id = PLATFORM_DEVID_NONE, >>> + .dev = { >>> + .dma_mask = &vchiq_device_dmamask, >>> + } >>> +}; >>> + >>> +static struct platform_device bcm2835_audio = { >>> + .name = "bcm2835_audio", >>> + .id = PLATFORM_DEVID_NONE, >>> + .dev = { >>> + .dma_mask = &vchiq_device_dmamask, >>> + } >>> + >> Extra blank line.
oops, checkpatch.pl didn't catch this :-/ >> >>> +}; >>> + >>> +static struct platform_device *vchiq_devices[] __initdata = { >> Make it const. >> >>> + &bcm2835_camera, >>> + &bcm2835_audio, >>> +}; >>> >>> struct vchiq_drvdata { >>> const unsigned int cache_line_size; >>> @@ -1763,28 +1784,6 @@ static const struct of_device_id vchiq_of_match[] = { >>> }; >>> MODULE_DEVICE_TABLE(of, vchiq_of_match); >>> >>> -static struct platform_device * >>> -vchiq_register_child(struct platform_device *pdev, const char *name) >>> -{ >>> - struct platform_device_info pdevinfo; >>> - struct platform_device *child; >>> - >>> - memset(&pdevinfo, 0, sizeof(pdevinfo)); >>> - >>> - pdevinfo.parent = &pdev->dev; >>> - pdevinfo.name = name; >>> - pdevinfo.id = PLATFORM_DEVID_NONE; >>> - pdevinfo.dma_mask = DMA_BIT_MASK(32); >>> - >>> - child = platform_device_register_full(&pdevinfo); >>> - if (IS_ERR(child)) { >>> - dev_warn(&pdev->dev, "%s not registered\n", name); >>> - child = NULL; >>> - } >>> - >>> - return child; >>> -} >>> - >>> static int vchiq_probe(struct platform_device *pdev) >>> { >>> struct device_node *fw_node; >>> @@ -1832,8 +1831,11 @@ static int vchiq_probe(struct platform_device *pdev) >>> goto error_exit; >>> } >>> >>> - bcm2835_camera = vchiq_register_child(pdev, "bcm2835-camera"); >>> - bcm2835_audio = vchiq_register_child(pdev, "bcm2835_audio"); >>> + err = platform_add_devices(vchiq_devices, ARRAY_SIZE(vchiq_devices)); >>> + if (err) { >>> + dev_warn(&pdev->dev, "Failed to add vchiq child devices"); >>> + goto error_exit; >>> + } >> If you unbind and rebind this driver, the platform_device instances >> defined as global variables will be reused, and I'm pretty sure that >> will cause issues, for instance with the kobj->state_initialized check >> in kobject_init() (called from device_initialize(), itself called from >> platform_device_register(), from platform_add_devices()). I'm not sure >> static instances of platform_device are a very good idea in general. > static instances of any device are a horrible idea, but it seems that > many drivers do this and abuse platform devices this way :(
It seems I have been a victim of the abuse usage while looking for platform_device references in the codebase. I'm working on a new approach for this.
Currently (as per the linux-next branch), the vchiq driver will happily carry on if any of the child platform device registration fails. That means if bcm2835-audio fails to register, bcm2835-camera will still kept registered I suppose.
However with usage of platform_add_devices() in this patch, I introduced a functionality change (I'm realizing this now) - any failure of child platform device registeration will -unregister- all the other platform devices i.e. if bcm2835-audio fails, bcm2835-camera will also get unregistered.
Should I be working towards the status-quo behavior ? Or it's sane to unregistered other platform devices if one of the fails like platform_add_devices() does ? (This affects my new approach as well, hence the question) > > Ideally this should be done properly, with the correct devices created > automatically based on the device tree structure, NOT hard-coded into a > .c file like this. > > So I too really do not like this change, why are these not being created > by the firware layer automatically?
Not sure if this is a helpful comment, but as far I know, there can be vchiq child platform devices which probably don't have a Device tree entry. like the bcm2835-isp [1] I posted earlier.
[1] https://lore.kernel.org/lkml/20221121214722.22563-1-umang.jain@ideasonboard.com/ > > thanks, > > greg k-h
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