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

[Umang Jain <umang.jain@xxxxxxxxxxxxxxxx>]

Hi Laurent,

On 22/03/24 1:20 am, Laurent Pinchart wrote:
> 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 ?

Seems essential to me looking at vchiq_get_state() helper

Especially in the vchiq_open() to get a starting state when the char 
device is opened..
> > No functional changes intended in this patch.
> >
> > Signed-off-by: Umang Jain <umang.jain@xxxxxxxxxxxxxxxx>
> > ---
> >   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 {