Re: [PATCH 2/2] staging: vc04_services: Replace dmac_map_area with dmac_map_sg

[Eric Anholt]

Michael Zoran <mzoran@xxxxxxxxxxxx> writes:

> On Tue, 2016-10-25 at 08:00 -0700, Michael Zoran wrote:
>> On Mon, 2016-10-24 at 10:31 -0700, Eric Anholt wrote:
>> > mzoran@xxxxxxxxxxxx writes:
>> > 
>> > > Â*/
>> > > Â
>> > > Âstatic int
>> > > Âcreate_pagelist(char __user *buf, size_t count, unsigned short
>> > > type,
>> > > -	struct task_struct *task, PAGELIST_T ** ppagelist)
>> > > +		struct task_struct *task, PAGELIST_T
>> > > **ppagelist,
>> > > +		dma_addr_t *dma_addr)
>> > > Â{
>> > > Â	PAGELIST_T *pagelist;
>> > > Â	struct page **pages;
>> > > -	unsigned long *addrs;
>> > > -	unsigned int num_pages, offset, i;
>> > > -	char *addr, *base_addr, *next_addr;
>> > > -	int run, addridx, actual_pages;
>> > > +	u32 *addrs;
>> > > +	unsigned int num_pages, offset, i, j, k;
>> > > +	int actual_pages;
>> > > ÂÂÂÂÂÂÂÂÂunsigned long *need_release;
>> > > +	size_t pagelist_size;
>> > > +	struct scatterlist *scatterlist;
>> > > +	int dma_buffers;
>> > > +	int dir;
>> > > Â
>> > > -	offset = (unsigned int)buf & (PAGE_SIZE - 1);
>> > > +	offset = ((unsigned int)(unsigned long)buf & (PAGE_SIZE
>> > > -
>> > > 1));
>> > > Â	num_pages = (count + offset + PAGE_SIZE - 1) /
>> > > PAGE_SIZE;
>> > > Â
>> > > +	pagelist_size = sizeof(PAGELIST_T) +
>> > > +			(num_pages * sizeof(unsigned long)) +
>> > > +			sizeof(unsigned long) +
>> > > +			(num_pages * sizeof(pages[0]) +
>> > > +			(num_pages * sizeof(struct
>> > > scatterlist)));
>> > > +
>> > > Â	*ppagelist = NULL;
>> > > Â
>> > > +	dir = (type == PAGELIST_WRITE) ? DMA_TO_DEVICE :
>> > > DMA_FROM_DEVICE;
>> > > +
>> > > Â	/* Allocate enough storage to hold the page pointers and
>> > > the page
>> > > Â	** list
>> > > Â	*/
>> > > -	pagelist = kmalloc(sizeof(PAGELIST_T) +
>> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ(num_pages * sizeof(unsigned long)) +
>> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂsizeof(unsigned long) +
>> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ(num_pages * sizeof(pages[0])),
>> > > -ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂGFP_KERNEL);
>> > > +	pagelist = dma_zalloc_coherent(g_dev,
>> > > +				ÂÂÂÂÂÂÂpagelist_size,
>> > > +				ÂÂÂÂÂÂÂdma_addr,
>> > > +				ÂÂÂÂÂÂÂGFP_KERNEL);
>> > > Â
>> > > Â	vchiq_log_trace(vchiq_arm_log_level, "create_pagelist -
>> > > %pK",
>> > > Â			pagelist);
>> > > @@ -394,10 +399,9 @@ create_pagelist(char __user *buf, size_t
>> > > count, unsigned short type,
>> > > Â	addrs = pagelist->addrs;
>> > > ÂÂÂÂÂÂÂÂÂneed_release = (unsigned long *)(addrs + num_pages);
>> > > Â	pages = (struct page **)(addrs + num_pages + 1);
>> > > +	scatterlist = (struct scatterlist *)(pages + num_pages);
>> > > Â
>> > > Â	if (is_vmalloc_addr(buf)) {
>> > > -		int dir = (type == PAGELIST_WRITE) ?
>> > > -			DMA_TO_DEVICE : DMA_FROM_DEVICE;
>> > > Â		unsigned long length = count;
>> > > Â		unsigned int off = offset;
>> > > Â
>> > > @@ -410,7 +414,6 @@ create_pagelist(char __user *buf, size_t
>> > > count,
>> > > unsigned short type,
>> > > Â			if (bytes > length)
>> > > Â				bytes = length;
>> > > Â			pages[actual_pages] = pg;
>> > > -			dmac_map_area(page_address(pg) + off,
>> > > bytes, dir);
>> > > Â			length -= bytes;
>> > > Â			off = 0;
>> > > Â		}
>> > > @@ -438,7 +441,8 @@ create_pagelist(char __user *buf, size_t
>> > > count,
>> > > unsigned short type,
>> > > Â				actual_pages--;
>> > > Â				put_page(pages[actual_pages]);
>> > > Â			}
>> > > -			kfree(pagelist);
>> > > +			dma_free_coherent(g_dev, pagelist_size,
>> > > +					ÂÂpagelist, *dma_addr);
>> > > Â			if (actual_pages == 0)
>> > > Â				actual_pages = -ENOMEM;
>> > > Â			return actual_pages;
>> > > @@ -450,29 +454,38 @@ create_pagelist(char __user *buf, size_t
>> > > count, unsigned short type,
>> > > Â	pagelist->type = type;
>> > > Â	pagelist->offset = offset;
>> > > Â
>> > > -	/* Group the pages into runs of contiguous pages */
>> > > -
>> > > -	base_addr = VCHIQ_ARM_ADDRESS(page_address(pages[0]));
>> > > -	next_addr = base_addr + PAGE_SIZE;
>> > > -	addridx = 0;
>> > > -	run = 0;
>> > > -
>> > > -	for (i = 1; i < num_pages; i++) {
>> > > -		addr =
>> > > VCHIQ_ARM_ADDRESS(page_address(pages[i]));
>> > > -		if ((addr == next_addr) && (run < (PAGE_SIZE -
>> > > 1))) {
>> > > -			next_addr += PAGE_SIZE;
>> > > -			run++;
>> > > -		} else {
>> > > -			addrs[addridx] = (unsigned
>> > > long)base_addr
>> > > + run;
>> > > -			addridx++;
>> > > -			base_addr = addr;
>> > > -			next_addr = addr + PAGE_SIZE;
>> > > -			run = 0;
>> > > -		}
>> > > +	for (i = 0; i < num_pages; i++)
>> > > +		sg_set_page(scatterlist + i, pages[i],
>> > > PAGE_SIZE,
>> > > 0);
>> > > +
>> > > +	dma_buffers = dma_map_sg(g_dev,
>> > > +				Âscatterlist,
>> > > +				Ânum_pages,
>> > > +				Âdir);
>> > > +
>> > > +	if (dma_buffers == 0) {
>> > > +		dma_free_coherent(g_dev, pagelist_size,
>> > > +				ÂÂpagelist, *dma_addr);
>> > > +
>> > > +		return -EINTR;
>> > > Â	}
>> > > Â
>> > > -	addrs[addridx] = (unsigned long)base_addr + run;
>> > > -	addridx++;
>> > > +	k = 0;
>> > > +	for (i = 0; i < dma_buffers;) {
>> > > +		u32 section_length = 0;
>> > > +
>> > > +		for (j = i + 1; j < dma_buffers; j++) {
>> > > +			if (sg_dma_address(scatterlist + j) !=
>> > > +			ÂÂÂÂsg_dma_address(scatterlist + j - 1)
>> > > +
>> > > PAGE_SIZE) {
>> > > +				break;
>> > > +			}
>> > > +			section_length++;
>> > > +		}
>> > > +
>> > > +		addrs[k] = (u32)sg_dma_address(scatterlist + i)
>> > > |
>> > > +				section_length;
>> > 
>> > It looks like scatterlist may not be just an array, so I think this
>> > whole loop wants to be something like:
>> > 
>> > for_each_sg(scatterlist, sg, num_pages, i) {
>> > 	u32 len = sg_dma_len(sg);
>> > ÂÂÂÂÂÂÂÂu32 addr = sg_dma_address(sg);
>> > 
>> > ÂÂÂÂÂÂÂÂif (k > 0 && addrs[k - 1] & PAGE_MASK +
>> > ÂÂÂÂÂÂÂÂÂÂÂÂ(addrs[k - 1] & ~PAGE_MASK) << PAGE_SHIFT) == addr) {
>> > ÂÂÂÂÂÂÂÂ	addrs[k - 1] += len;
>> > ÂÂÂÂÂÂÂÂ} else {
>> > ÂÂÂÂÂÂÂÂ	addrs[k++] = addr | len;
>> > ÂÂÂÂÂÂÂÂ}
>> > }
>> > 
>> > Note the use of sg_dma_len(), since sg entries may be more than one
>> > page.ÂÂI don't think any merging is actually happening on our
>> > platform
>> > currently, thus why I left the inner loop.
>> > 
>> > Thanks for taking on doing this conversion!ÂÂThis code's going to
>> > be
>> > so
>> > much nicer when you're done.
>> 
>> Thanks for looking at this. Â
>> 
>> While I understand the use of sg_dma_len, I don't understand totally
>> the need for "for_each_sg". The scatterlist can be part of a scatter
>> table with all kinds of complex chaining, but in this case it is
>> directly allocated as an array at the top of the function.
>> 
>> Also note that the addrs[] list is passed to the firmware and it
>> requires all the items of the list be paged aligned and be a multiple
>> of the page size.ÂÂSo I'm also a bit confused about the need for
>> handling scatterlists that are not page aligned or a multiple of
>> pages.

I'm sure we can assume that sg_dma_map is going to give us back
page-aligned mappings, because we only asked for page aligned mappings.

I'm just making suggestions that follow what is describeed in
DMA-API-HOWTO.txt here.  Following the documentation seems like a good
idea unless there's a reason not to.

> Sorry, but I forgot to add that the addrs list is a address anded with
> a page count, not a byte count.   The example you have sent appears at
> a glance to look like it is anding a byte count with the address.

Looking at the type of the field being read, it looked like a page count
to me, but I was unsure and the header didn't clarify.  Looking again,
it must be bytes, so shifting would be necessary.

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