Re: [PATCH RESEND v10 07/11] device-mapping: Introduce DMA range map, supplanting dma_pfn_offset

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Mon, Aug 17, 2020 at 05:53:09PM -0400, Jim Quinlan wrote:
> The new field 'dma_range_map' in struct device is used to facilitate the
> use of single or multiple offsets between mapping regions of cpu addrs and
> dma addrs.  It subsumes the role of "dev->dma_pfn_offset" which was only
> capable of holding a single uniform offset and had no region bounds
> checking.
> 
> The function of_dma_get_range() has been modified so that it takes a single
> argument -- the device node -- and returns a map, NULL, or an error code.
> The map is an array that holds the information regarding the DMA regions.
> Each range entry contains the address offset, the cpu_start address, the
> dma_start address, and the size of the region.
> 
> of_dma_configure() is the typical manner to set range offsets but there are
> a number of ad hoc assignments to "dev->dma_pfn_offset" in the kernel
> driver code.  These cases now invoke the function
> dma_attach_offset_range(dev, cpu_addr, dma_addr, size).

...

> +	if (dev) {
> +		phys_addr_t paddr = PFN_PHYS(pfn);
> +

> +		pfn -= (dma_offset_from_phys_addr(dev, paddr) >> PAGE_SHIFT);

PFN_DOWN() ?

> +	}

...

> +		pfn += (dma_offset_from_dma_addr(dev, addr) >> PAGE_SHIFT);

Ditto.


...

> +static inline u64 dma_offset_from_dma_addr(struct device *dev, dma_addr_t dma_addr)
> +{
> +	const struct bus_dma_region *m = dev->dma_range_map;
> +
> +	if (!m)
> +		return 0;
> +	for (; m->size; m++)
> +		if (dma_addr >= m->dma_start && dma_addr - m->dma_start < m->size)
> +			return m->offset;
> +	return 0;
> +}
> +
> +static inline u64 dma_offset_from_phys_addr(struct device *dev, phys_addr_t paddr)
> +{
> +	const struct bus_dma_region *m = dev->dma_range_map;
> +
> +	if (!m)
> +		return 0;
> +	for (; m->size; m++)
> +		if (paddr >= m->cpu_start && paddr - m->cpu_start < m->size)
> +			return m->offset;
> +	return 0;
> +}

Perhaps for these the form with one return 0 is easier to read

	if (m) {
		for (; m->size; m++)
			if (paddr >= m->cpu_start && paddr - m->cpu_start < m->size)
				return m->offset;
	}
	return 0;

?

...

> +	if (mem->use_dev_dma_pfn_offset) {
> +		u64 base_addr = (u64)mem->pfn_base << PAGE_SHIFT;

PFN_PHYS() ?

> +
> +		return base_addr - dma_offset_from_phys_addr(dev, base_addr);
> +	}

...

> + * It returns -ENOMEM if out of memory, 0 otherwise.

This doesn't describe cases dev->dma_range_map != NULL and offset == 0.

> +int dma_set_offset_range(struct device *dev, phys_addr_t cpu_start,
> +			 dma_addr_t dma_start, u64 size)
> +{
> +	struct bus_dma_region *map;
> +	u64 offset = (u64)cpu_start - (u64)dma_start;
> +
> +	if (!offset)
> +		return 0;
> +
> +	if (dev->dma_range_map) {
> +		dev_err(dev, "attempt to add DMA range to existing map\n");
> +		return -EINVAL;
> +	}
> +
> +	map = kcalloc(2, sizeof(*map), GFP_KERNEL);
> +	if (!map)
> +		return -ENOMEM;
> +	map[0].cpu_start = cpu_start;
> +	map[0].dma_start = dma_start;
> +	map[0].offset = offset;
> +	map[0].size = size;
> +	dev->dma_range_map = map;
> +
> +	return 0;
> +}

...

> +void *dma_copy_dma_range_map(const struct bus_dma_region *map)
> +{
> +	int num_ranges;
> +	struct bus_dma_region *new_map;
> +	const struct bus_dma_region *r = map;
> +
> +	for (num_ranges = 0; r->size; num_ranges++)
> +		r++;

> +	new_map = kcalloc(num_ranges + 1, sizeof(*map), GFP_KERNEL);
> +	if (new_map)
> +		memcpy(new_map, map, sizeof(*map) * num_ranges);

Looks like krealloc() on the first glance...

> +
> +	return new_map;
> +}

-- 
With Best Regards,
Andy Shevchenko


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