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

[Umang Jain <umang.jain@ideasonboard.com>]

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@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 {