Re: [RFC PATCH V6 2/7] drm/gpu: Add gpu_buddy_addr_to_block helper

[Matthew Auld <matthew.auld@intel.com>]

On 02/04/2026 01:09, Matthew Brost wrote:
> On Fri, Mar 27, 2026 at 05:18:15PM +0530, Tejas Upadhyay wrote:
>> Add helper with primary purpose is to efficiently trace a specific
>> physical memory address back to its corresponding TTM buffer object.
>>
>> Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
>> ---
>>   drivers/gpu/buddy.c       | 56 +++++++++++++++++++++++++++++++++++++++
>>   include/linux/gpu_buddy.h |  2 ++
>>   2 files changed, 58 insertions(+)
>>
>> diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c
>> index 52686672e99f..2d26c2a0f971 100644
>> --- a/drivers/gpu/buddy.c
>> +++ b/drivers/gpu/buddy.c
>> @@ -589,6 +589,62 @@ void gpu_buddy_free_block(struct gpu_buddy *mm,
>>   }
>>   EXPORT_SYMBOL(gpu_buddy_free_block);
>>   
>> +/**
>> + * gpu_buddy_addr_to_block - given physical address find a block
>> + *
>> + * @mm: GPU buddy manager
>> + * @addr: Physical address
>> + *
>> + * Returns:
>> + * gpu_buddy_block on success, NULL or error code on failure
>> + */
>> +struct gpu_buddy_block *gpu_buddy_addr_to_block(struct gpu_buddy *mm, u64 addr)
>> +{
>> +	struct gpu_buddy_block *block;
>> +	LIST_HEAD(dfs);
>> +	u64 end;
>> +	int i;
>> +
> 
> This is somewhat of an orthogonal issue, but we really should update
> gpu_buddy so drivers can register a lock that we can assert is held in
> functions where gpu_buddy manipulates blocks.
> 
> Something like this [1].

I think would be a good addition also.

> 
> I’ll defer to the gpu_buddy maintainers on whether this code is correct.
> 
> Matt
> 
> [1] https://elixir.bootlin.com/linux/v6.19.10/source/include/drm/drm_gpusvm.h#L341
> 
>> +	end = addr + SZ_4K - 1;
>> +	for (i = 0; i < mm->n_roots; ++i)
>> +		list_add_tail(&mm->roots[i]->tmp_link, &dfs);
>> +
>> +	do {
>> +		u64 block_start;
>> +		u64 block_end;
>> +
>> +		block = list_first_entry_or_null(&dfs,
>> +						 struct gpu_buddy_block,
>> +						 tmp_link);
>> +		if (!block)
>> +			break;
>> +
>> +		list_del(&block->tmp_link);
>> +
>> +		block_start = gpu_buddy_block_offset(block);
>> +		block_end = block_start + gpu_buddy_block_size(mm, block) - 1;
>> +
>> +		if (!overlaps(addr, end, block_start, block_end))
>> +			continue;
>> +
>> +		if (contains(addr, end, block_start, block_end) &&
>> +		    !gpu_buddy_block_is_split(block)) {
>> +			if (gpu_buddy_block_is_free(block))
>> +				return NULL;
>> +			else if (gpu_buddy_block_is_allocated(block) && !mm->clear_avail)
>> +				return block;
>> +		}
>> +
>> +		if (gpu_buddy_block_is_split(block)) {
>> +			list_add(&block->right->tmp_link, &dfs);
>> +			list_add(&block->left->tmp_link, &dfs);
>> +		}
>> +	} while (1);
>> +
>> +	return ERR_PTR(-ENXIO);
>> +}
>> +EXPORT_SYMBOL(gpu_buddy_addr_to_block);
>> +
>>   static void __gpu_buddy_free_list(struct gpu_buddy *mm,
>>   				  struct list_head *objects,
>>   				  bool mark_clear,
>> diff --git a/include/linux/gpu_buddy.h b/include/linux/gpu_buddy.h
>> index 5fa917ba5450..957c69c560bc 100644
>> --- a/include/linux/gpu_buddy.h
>> +++ b/include/linux/gpu_buddy.h
>> @@ -231,6 +231,8 @@ void gpu_buddy_reset_clear(struct gpu_buddy *mm, bool is_clear);
>>   
>>   void gpu_buddy_free_block(struct gpu_buddy *mm, struct gpu_buddy_block *block);
>>   
>> +struct gpu_buddy_block *gpu_buddy_addr_to_block(struct gpu_buddy *mm, u64 addr);
>> +
>>   void gpu_buddy_free_list(struct gpu_buddy *mm,
>>   			 struct list_head *objects,
>>   			 unsigned int flags);
>> -- 
>> 2.52.0
>>