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SubjectRe: [PATCH 2/2] staging: vc04_services: Replace dmac_map_area with dmac_map_sg
From
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On Mon, 2016-10-24 at 10:31 -0700, Eric Anholt wrote:
> mzoran@crowfest.net writes:
>
> >  */
> >  
> >  static int
> >  create_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)
> >  {
> >   PAGELIST_T *pagelist;
> >   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;
> >          unsigned long *need_release;
> > + size_t pagelist_size;
> > + struct scatterlist *scatterlist;
> > + int dma_buffers;
> > + int dir;
> >  
> > - offset = (unsigned int)buf & (PAGE_SIZE - 1);
> > + offset = ((unsigned int)(unsigned long)buf & (PAGE_SIZE -
> > 1));
> >   num_pages = (count + offset + PAGE_SIZE - 1) / PAGE_SIZE;
> >  
> > + pagelist_size = sizeof(PAGELIST_T) +
> > + (num_pages * sizeof(unsigned long)) +
> > + sizeof(unsigned long) +
> > + (num_pages * sizeof(pages[0]) +
> > + (num_pages * sizeof(struct scatterlist)));
> > +
> >   *ppagelist = NULL;
> >  
> > + dir = (type == PAGELIST_WRITE) ? DMA_TO_DEVICE :
> > DMA_FROM_DEVICE;
> > +
> >   /* Allocate enough storage to hold the page pointers and
> > the page
> >   ** list
> >   */
> > - pagelist = kmalloc(sizeof(PAGELIST_T) +
> > -                           (num_pages * sizeof(unsigned long)) +
> > -                           sizeof(unsigned long) +
> > -                           (num_pages * sizeof(pages[0])),
> > -                           GFP_KERNEL);
> > + pagelist = dma_zalloc_coherent(g_dev,
> > +        pagelist_size,
> > +        dma_addr,
> > +        GFP_KERNEL);
> >  
> >   vchiq_log_trace(vchiq_arm_log_level, "create_pagelist -
> > %pK",
> >   pagelist);
> > @@ -394,10 +399,9 @@ create_pagelist(char __user *buf, size_t
> > count, unsigned short type,
> >   addrs = pagelist->addrs;
> >          need_release = (unsigned long *)(addrs + num_pages);
> >   pages = (struct page **)(addrs + num_pages + 1);
> > + scatterlist = (struct scatterlist *)(pages + num_pages);
> >  
> >   if (is_vmalloc_addr(buf)) {
> > - int dir = (type == PAGELIST_WRITE) ?
> > - DMA_TO_DEVICE : DMA_FROM_DEVICE;
> >   unsigned long length = count;
> >   unsigned int off = offset;
> >  
> > @@ -410,7 +414,6 @@ create_pagelist(char __user *buf, size_t count,
> > unsigned short type,
> >   if (bytes > length)
> >   bytes = length;
> >   pages[actual_pages] = pg;
> > - dmac_map_area(page_address(pg) + off,
> > bytes, dir);
> >   length -= bytes;
> >   off = 0;
> >   }
> > @@ -438,7 +441,8 @@ create_pagelist(char __user *buf, size_t count,
> > unsigned short type,
> >   actual_pages--;
> >   put_page(pages[actual_pages]);
> >   }
> > - kfree(pagelist);
> > + dma_free_coherent(g_dev, pagelist_size,
> > +   pagelist, *dma_addr);
> >   if (actual_pages == 0)
> >   actual_pages = -ENOMEM;
> >   return actual_pages;
> > @@ -450,29 +454,38 @@ create_pagelist(char __user *buf, size_t
> > count, unsigned short type,
> >   pagelist->type = type;
> >   pagelist->offset = offset;
> >  
> > - /* 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,
> > +  scatterlist,
> > +  num_pages,
> > +  dir);
> > +
> > + if (dma_buffers == 0) {
> > + dma_free_coherent(g_dev, pagelist_size,
> > +   pagelist, *dma_addr);
> > +
> > + return -EINTR;
> >   }
> >  
> > - 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) !=
> > +     sg_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);
>         u32 addr = sg_dma_address(sg);
>
>         if (k > 0 && addrs[k - 1] & PAGE_MASK +
>             (addrs[k - 1] & ~PAGE_MASK) << PAGE_SHIFT) == addr) {
>          addrs[k - 1] += len;
>         } else {
>          addrs[k++] = addr | len;
>         }
> }
>
> Note the use of sg_dma_len(), since sg entries may be more than one
> page.  I 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!  This code's going to be
> so
> much nicer when you're done.

Thanks for looking at this.  

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. So I'm also a bit confused about the need for
handling scatterlists that are not page aligned or a multiple of pages.





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