linux-kernel - Re: [PATCHv4 5/5] arm64: Add atomic pool for non-coherent and CMA allocations.

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Date:	Mon, 21 Jul 2014 15:00:52 -0700
From:	Laura Abbott <lauraa@...eaurora.org>
To:	Thierry Reding <thierry.reding@...il.com>
CC:	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	David Riley <davidriley@...omium.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Ritesh Harjain <ritesh.harjani@...il.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCHv4 5/5] arm64: Add atomic pool for non-coherent and CMA
 allocations.

On 7/4/2014 6:35 AM, Thierry Reding wrote:
> On Wed, Jul 02, 2014 at 11:03:38AM -0700, Laura Abbott wrote:
> [...]
>> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> [...]
>> +static struct gen_pool *atomic_pool;
>> +
>> +#define DEFAULT_DMA_COHERENT_POOL_SIZE  SZ_256K
>> +static size_t atomic_pool_size = DEFAULT_DMA_COHERENT_POOL_SIZE;
> 
> There doesn't seem to be much use for this since it can't be overridden
> via init_dma_coherent_pool_size like on ARM.
> 

There is still the command line option coherent_pool=<size> though

[...]
>> +	if (page) {
>> +		int ret;
>> +
>> +		atomic_pool = gen_pool_create(PAGE_SHIFT, -1);
>> +		if (!atomic_pool)
>> +			goto free_page;
>> +
>> +		addr = dma_common_contiguous_remap(page, atomic_pool_size,
>> +					VM_USERMAP, prot, atomic_pool_init);
>> +
>> +		if (!addr)
>> +			goto destroy_genpool;
>> +
>> +		memset(addr, 0, atomic_pool_size);
>> +		__dma_flush_range(addr, addr + atomic_pool_size);
>> +
>> +		ret = gen_pool_add_virt(atomic_pool, (unsigned long)addr,
>> +					page_to_phys(page),
>> +					atomic_pool_size, -1);
>> +		if (ret)
>> +			goto remove_mapping;
>> +
>> +		gen_pool_set_algo(atomic_pool,
>> +				  gen_pool_first_fit_order_align, NULL);
>> +
>> +		pr_info("DMA: preallocated %zd KiB pool for atomic allocations\n",
> 
> I think this should be "%zu" because atomic_pool_size is a size_t, not a
> ssize_t.
> 

Yes, will fix.

>> +			atomic_pool_size / 1024);
>> +		return 0;
>> +	}
>> +	goto out;
>> +
>> +remove_mapping:
>> +	dma_common_free_remap(addr, atomic_pool_size, VM_USERMAP);
>> +destroy_genpool:
>> +	gen_pool_destroy(atomic_pool);
>> +	atomic_pool == NULL;
> 
> This probably doesn't belong here.
> 

Dastardly typo.

>> +free_page:
>> +	if (!dma_release_from_contiguous(NULL, page, nr_pages))
>> +		__free_pages(page, get_order(atomic_pool_size));
> 
> You use get_order(atomic_pool_size) a lot, perhaps it should be a
> temporary variable?
> 

Yes, three usages is probably enough.

>> +out:
>> +	pr_err("DMA: failed to allocate %zx KiB pool for atomic coherent allocation\n",
>> +		atomic_pool_size / 1024);
> 
> Print in decimal rather than hexadecimal?
> 

I actually prefer hexadecimal but I should at least be consistent between
error and non-error paths.

> Thierry
> 

Thanks,
Laura

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