Re: [PATCH v3 5/6] staging: vc04_services: Drop global variables tracking allocated pages

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Uamng,

Thank you for the patch.

On Thu, Mar 21, 2024 at 04:07:39PM +0530, Umang Jain wrote:
> The variables tracking allocated pages fragments in vchiq_arm.c
> can be easily moved to struct vchiq_drv_mgmt instead of being global.
> This helps us to drop the non-essential global variables in the vchiq
> interface.
> 
> However, g_regs is intentionally kept global since it is read/write
> in fast paths (for e.g. doorbell IRQs). Introducing it in struct
> vchiq_drv_mgmt and getting it in remote_event_signal handler, turns
> out to be quite tedious. Add a comment for the same.

The fast path argument doesn't really hold in my opinion, I think you
can retrieve the variable through vchiq_state in vchiq_doorbell_irq().

All callers for remote_event_signal have a vchiq_state pointer, so it
shouldn't be that difficult to get rid of that global variable. It
doesn't have to be done in this patch, it can be done on top.

> 
> Drop the TODO item as well, as it is now totally addressed:
> > Get rid of all non essential global structures and create a proper per
>   device structure

Don't you need to also drop the g_state variable ?

> 
> No functional changes intended in this patch.
> 
> Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
> ---
>  drivers/staging/vc04_services/interface/TODO  |  8 ---
>  .../interface/vchiq_arm/vchiq_arm.c           | 57 +++++++++----------
>  .../interface/vchiq_arm/vchiq_arm.h           |  6 ++
>  3 files changed, 34 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/staging/vc04_services/interface/TODO b/drivers/staging/vc04_services/interface/TODO
> index 05eb5140d096..15f12b8f213e 100644
> --- a/drivers/staging/vc04_services/interface/TODO
> +++ b/drivers/staging/vc04_services/interface/TODO
> @@ -41,14 +41,6 @@ The code follows the 80 characters limitation yet tends to go 3 or 4 levels of
>  indentation deep making it very unpleasant to read. This is specially relevant
>  in the character driver ioctl code and in the core thread functions.
>  
> -* Get rid of all non essential global structures and create a proper per
> -device structure
> -
> -The first thing one generally sees in a probe function is a memory allocation
> -for all the device specific data. This structure is then passed all over the
> -driver. This is good practice since it makes the driver work regardless of the
> -number of devices probed.
> -
>  * Clean up Sparse warnings from __user annotations. See
>  vchiq_irq_queue_bulk_tx_rx(). Ensure that the address of "&waiter->bulk_waiter"
>  is never disclosed to userspace.
> 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 ba096bcb32c8..c4807b302718 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
> @@ -140,13 +140,11 @@ struct vchiq_pagelist_info {
>  	unsigned int scatterlist_mapped;
>  };
>  
> +/*
> + * Essential global pointer since read/written on fast paths
> + * (doorbell IRQs).
> + */
>  static void __iomem *g_regs;
> -static unsigned int g_fragments_size;
> -static char *g_fragments_base;
> -static char *g_free_fragments;
> -static struct semaphore g_free_fragments_sema;
> -
> -static DEFINE_SEMAPHORE(g_free_fragments_mutex, 1);

Why is this code using a semaphore as a mutex ?? It should be replaced
with a real mutex. This can be done on top of this patch.

>  
>  static int
>  vchiq_blocking_bulk_transfer(struct vchiq_instance *instance, unsigned int handle, void *data,
> @@ -377,20 +375,20 @@ create_pagelist(struct vchiq_instance *instance, char *buf, char __user *ubuf,
>  	    (drv_mgmt->pinfo->cache_line_size - 1)))) {
>  		char *fragments;
>  
> -		if (down_interruptible(&g_free_fragments_sema)) {
> +		if (down_interruptible(&drv_mgmt->free_fragments_sema)) {
>  			cleanup_pagelistinfo(instance, pagelistinfo);
>  			return NULL;
>  		}
>  
> -		WARN_ON(!g_free_fragments);
> +		WARN_ON(!drv_mgmt->free_fragments);
>  
> -		down(&g_free_fragments_mutex);
> -		fragments = g_free_fragments;
> +		down(&drv_mgmt->free_fragments_mutex);
> +		fragments = drv_mgmt->free_fragments;
>  		WARN_ON(!fragments);
> -		g_free_fragments = *(char **)g_free_fragments;
> -		up(&g_free_fragments_mutex);
> +		drv_mgmt->free_fragments = *(char **)drv_mgmt->free_fragments;
> +		up(&drv_mgmt->free_fragments_mutex);
>  		pagelist->type = PAGELIST_READ_WITH_FRAGMENTS +
> -			(fragments - g_fragments_base) / g_fragments_size;
> +			(fragments - drv_mgmt->fragments_base) / drv_mgmt->fragments_size;
>  	}
>  
>  	return pagelistinfo;
> @@ -420,10 +418,10 @@ free_pagelist(struct vchiq_instance *instance, struct vchiq_pagelist_info *pagel
>  	pagelistinfo->scatterlist_mapped = 0;
>  
>  	/* Deal with any partial cache lines (fragments) */
> -	if (pagelist->type >= PAGELIST_READ_WITH_FRAGMENTS && g_fragments_base) {
> -		char *fragments = g_fragments_base +
> +	if (pagelist->type >= PAGELIST_READ_WITH_FRAGMENTS && drv_mgmt->fragments_base) {
> +		char *fragments = drv_mgmt->fragments_base +
>  			(pagelist->type - PAGELIST_READ_WITH_FRAGMENTS) *
> -			g_fragments_size;
> +			drv_mgmt->fragments_size;
>  		int head_bytes, tail_bytes;
>  
>  		head_bytes = (drv_mgmt->pinfo->cache_line_size - pagelist->offset) &
> @@ -448,11 +446,11 @@ free_pagelist(struct vchiq_instance *instance, struct vchiq_pagelist_info *pagel
>  				fragments + drv_mgmt->pinfo->cache_line_size,
>  				tail_bytes);
>  
> -		down(&g_free_fragments_mutex);
> -		*(char **)fragments = g_free_fragments;
> -		g_free_fragments = fragments;
> -		up(&g_free_fragments_mutex);
> -		up(&g_free_fragments_sema);
> +		down(&drv_mgmt->free_fragments_mutex);
> +		*(char **)fragments = drv_mgmt->free_fragments;
> +		drv_mgmt->free_fragments = fragments;
> +		up(&drv_mgmt->free_fragments_mutex);
> +		up(&drv_mgmt->free_fragments_sema);
>  	}
>  
>  	/* Need to mark all the pages dirty. */
> @@ -488,11 +486,11 @@ static int vchiq_platform_init(struct platform_device *pdev, struct vchiq_state
>  	if (err < 0)
>  		return err;
>  
> -	g_fragments_size = 2 * drv_mgmt->pinfo->cache_line_size;
> +	drv_mgmt->fragments_size = 2 * drv_mgmt->pinfo->cache_line_size;
>  
>  	/* Allocate space for the channels in coherent memory */
>  	slot_mem_size = PAGE_ALIGN(TOTAL_SLOTS * VCHIQ_SLOT_SIZE);
> -	frag_mem_size = PAGE_ALIGN(g_fragments_size * MAX_FRAGMENTS);
> +	frag_mem_size = PAGE_ALIGN(drv_mgmt->fragments_size * MAX_FRAGMENTS);
>  
>  	slot_mem = dmam_alloc_coherent(dev, slot_mem_size + frag_mem_size,
>  				       &slot_phys, GFP_KERNEL);
> @@ -512,15 +510,16 @@ static int vchiq_platform_init(struct platform_device *pdev, struct vchiq_state
>  	vchiq_slot_zero->platform_data[VCHIQ_PLATFORM_FRAGMENTS_COUNT_IDX] =
>  		MAX_FRAGMENTS;
>  
> -	g_fragments_base = (char *)slot_mem + slot_mem_size;
> +	drv_mgmt->fragments_base = (char *)slot_mem + slot_mem_size;
>  
> -	g_free_fragments = g_fragments_base;
> +	drv_mgmt->free_fragments = drv_mgmt->fragments_base;
>  	for (i = 0; i < (MAX_FRAGMENTS - 1); i++) {
> -		*(char **)&g_fragments_base[i * g_fragments_size] =
> -			&g_fragments_base[(i + 1) * g_fragments_size];
> +		*(char **)&drv_mgmt->fragments_base[i * drv_mgmt->fragments_size] =
> +			&drv_mgmt->fragments_base[(i + 1) * drv_mgmt->fragments_size];
>  	}
> -	*(char **)&g_fragments_base[i * g_fragments_size] = NULL;
> -	sema_init(&g_free_fragments_sema, MAX_FRAGMENTS);
> +	*(char **)&drv_mgmt->fragments_base[i * drv_mgmt->fragments_size] = NULL;
> +	sema_init(&drv_mgmt->free_fragments_sema, MAX_FRAGMENTS);
> +	sema_init(&drv_mgmt->free_fragments_mutex, 1);
>  
>  	err = vchiq_init_state(state, vchiq_slot_zero, dev);
>  	if (err)
> diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h
> index 1190fab2efc4..1134187da6ab 100644
> --- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h
> +++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.h
> @@ -41,6 +41,12 @@ struct vchiq_drv_mgmt {
>  	bool connected;
>  	int num_deferred_callbacks;
>  	void (*deferred_callback[VCHIQ_DRV_MAX_CALLBACKS])(void);
> +
> +	struct semaphore free_fragments_sema;
> +	struct semaphore free_fragments_mutex;
> +	char *fragments_base;
> +	char *free_fragments;
> +	unsigned int fragments_size;
>  };
>  
>  struct user_service {

-- 
Regards,

Laurent Pinchart