Re: [PATCH v6 08/12] device core: Introduce DMA range map, supplanting dma_pfn_offset

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Jim Quinlan <james.quinlan@broadcom.com>
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Subject: Re: [PATCH v6 08/12] device core: Introduce DMA range map, supplanting dma_pfn_offset
Date: Thu, 2 Jul 2020 11:42:51 +0300	[thread overview]
Message-ID: <20200702084251.GF3703480@smile.fi.intel.com> (raw)
In-Reply-To: <20200701212155.37830-9-james.quinlan@broadcom.com>

On Wed, Jul 01, 2020 at 05:21:38PM -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 && dev->dma_range_map)
> +		pfn -= (unsigned long)PFN_DOWN(dma_offset_from_phys_addr(dev, PFN_PHYS(pfn)));

Instead of casting use PHYS_PFN() and it will be consistent with latter in the same line.

> +	if (dev && dev->dma_range_map)
> +		pfn += (unsigned long)PFN_DOWN(dma_offset_from_dma_addr(dev, addr));

Ditto.

...

> +		dev_err(dev, "set dma_offset%08llx%s\n", KEYSTONE_HIGH_PHYS_START
> +			- KEYSTONE_LOW_PHYS_START, ret ? " failed" : "");

Please, avoid such indentation.
Better split it to the three lines, argument per line (expect dev which will go
on the first one).

This applies to all similar places.

...

>  	unsigned long pfn = (dma_handle >> PAGE_SHIFT);

PHYS_PFN() / PFN_DOWN() ?

> +	if (!WARN_ON(!dev) && dev->dma_range_map)
> +		pfn += (unsigned long)PFN_DOWN(dma_offset_from_dma_addr(dev, dma_handle));

PHYS_PFN() ?

...

> +	r = kcalloc(num_ranges + 1, sizeof(struct bus_dma_region), GFP_KERNEL);

sizeof(*r) ?

> +	if (!r)
> +		return ERR_PTR(-ENOMEM);

...

> +	ret = IS_ERR(map) ? PTR_ERR(map) : 0;

PTR_ERR_OR_ZERO()

...

> +		/* We want the offset map to be device-managed, so alloc & copy */
> +		dev->dma_range_map = devm_kcalloc(dev, num_ranges + 1, sizeof(*r),
> +						  GFP_KERNEL);

The question is how many times per device lifetime this can be called?

...

> +		if (!dev->dma_range_map)
> +			return -ENOMEM;
> +		memcpy((void *)dev->dma_range_map, map, sizeof(*r) * num_ranges + 1);

If it's continuous, perhaps kmemdup() ?

...

> +	rc = IS_ERR(map) ? PTR_ERR(map) : 0;

PTR_ERR_OR_ZERO()

...

> +			= dma_offset_from_phys_addr(dev, PFN_PHYS(mem->pfn_base));
> +
> +		return (dma_addr_t)PFN_PHYS(mem->pfn_base) - dma_offset;

Looking at this more, I think you need to introduce in the same header (pfn.h)
something like:

	#define PFN_DMA_ADDR()
	#define DMA_ADDR_PFN()

-- 
With Best Regards,
Andy Shevchenko

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