Re: [PATCH] misc: sram: Add dma-heap-export reserved SRAM area type

[John Stultz]

On Fri, Apr 24, 2020 at 3:27 PM Andrew F. Davis <afd@xxxxxx> wrote:
> This new export type exposes to userspace the SRAM area as a DMA-Heap,
> this allows for allocations as DMA-BUFs that can be consumed by various
> DMA-BUF supporting devices.
>
> Signed-off-by: Andrew F. Davis <afd@xxxxxx>

Nice! Very excited to have the first new heap (that didn't come with
the initial patchset)!

Overall looks good! I don't have any comment on the SRAM side of
things, but a few minor questions/nits below.

> diff --git a/drivers/misc/sram-dma-heap.c b/drivers/misc/sram-dma-heap.c
> new file mode 100644
> index 000000000000..38df0397f294
> --- /dev/null
> +++ b/drivers/misc/sram-dma-heap.c
> @@ -0,0 +1,243 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * SRAM DMA-Heap userspace exporter
> + *
> + * Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
> + *     Andrew F. Davis <afd@xxxxxx>
> + */
> +
> +#include <linux/dma-mapping.h>
> +#include <linux/err.h>
> +#include <linux/genalloc.h>
> +#include <linux/io.h>
> +#include <linux/mm.h>
> +#include <linux/scatterlist.h>
> +#include <linux/slab.h>
> +#include <linux/dma-buf.h>
> +#include <linux/dma-heap.h>
> +
> +#include "sram.h"
> +
> +struct sram_dma_heap {
> +       struct dma_heap *heap;
> +       struct gen_pool *pool;
> +};
> +
> +struct sram_dma_heap_buffer {
> +       struct gen_pool *pool;
> +       struct list_head attachments;
> +       struct mutex attachments_lock;
> +       unsigned long len;
> +       void *vaddr;
> +       phys_addr_t paddr;
> +};
> +
> +struct dma_heap_attachment {
> +       struct device *dev;
> +       struct sg_table *table;
> +       struct list_head list;
> +};
> +
> +static int dma_heap_attach(struct dma_buf *dmabuf,
> +                          struct dma_buf_attachment *attachment)
> +{
> +       struct sram_dma_heap_buffer *buffer = dmabuf->priv;
> +       struct dma_heap_attachment *a;
> +       struct sg_table *table;
> +
> +       a = kzalloc(sizeof(*a), GFP_KERNEL);
> +       if (!a)
> +               return -ENOMEM;
> +
> +       table = kmalloc(sizeof(*table), GFP_KERNEL);
> +       if (!table) {
> +               kfree(a);
> +               return -ENOMEM;
> +       }
> +       if (sg_alloc_table(table, 1, GFP_KERNEL)) {
> +               kfree(table);
> +               kfree(a);
> +               return -ENOMEM;
> +       }
> +       sg_set_page(table->sgl, pfn_to_page(PFN_DOWN(buffer->paddr)), buffer->len, 0);
> +
> +       a->table = table;
> +       a->dev = attachment->dev;
> +       INIT_LIST_HEAD(&a->list);
> +
> +       attachment->priv = a;
> +
> +       mutex_lock(&buffer->attachments_lock);
> +       list_add(&a->list, &buffer->attachments);
> +       mutex_unlock(&buffer->attachments_lock);
> +
> +       return 0;
> +}
> +
> +static void dma_heap_detatch(struct dma_buf *dmabuf,
> +                            struct dma_buf_attachment *attachment)
> +{
> +       struct sram_dma_heap_buffer *buffer = dmabuf->priv;
> +       struct dma_heap_attachment *a = attachment->priv;
> +
> +       mutex_lock(&buffer->attachments_lock);
> +       list_del(&a->list);
> +       mutex_unlock(&buffer->attachments_lock);
> +
> +       sg_free_table(a->table);
> +       kfree(a->table);
> +       kfree(a);
> +}
> +
> +static struct sg_table *dma_heap_map_dma_buf(struct dma_buf_attachment *attachment,
> +                                            enum dma_data_direction direction)
> +{
> +       struct dma_heap_attachment *a = attachment->priv;
> +       struct sg_table *table = a->table;
> +
> +       if (!dma_map_sg_attrs(attachment->dev, table->sgl, table->nents,
> +                             direction, DMA_ATTR_SKIP_CPU_SYNC))

Might be nice to have a comment as to why you're using SKIP_CPU_SYNC
and why it's safe.

> +               return ERR_PTR(-ENOMEM);
> +
> +       return table;
> +}
> +
> +static void dma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
> +                                  struct sg_table *table,
> +                                  enum dma_data_direction direction)
> +{
> +       dma_unmap_sg_attrs(attachment->dev, table->sgl, table->nents,
> +                          direction, DMA_ATTR_SKIP_CPU_SYNC);
> +}
> +
> +static void dma_heap_dma_buf_release(struct dma_buf *dmabuf)
> +{
> +       struct sram_dma_heap_buffer *buffer = dmabuf->priv;
> +
> +       gen_pool_free(buffer->pool, (unsigned long)buffer->vaddr, buffer->len);
> +       kfree(buffer);
> +}
> +
> +static int dma_heap_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma)
> +{
> +       struct sram_dma_heap_buffer *buffer = dmabuf->priv;
> +       int ret;
> +
> +       /* SRAM mappings are not cached */
> +       vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
> +
> +       ret = vm_iomap_memory(vma, buffer->paddr, buffer->len);
> +       if (ret)
> +               pr_err("Could not map buffer to userspace\n");
> +
> +       return ret;
> +}
> +
> +static void *dma_heap_vmap(struct dma_buf *dmabuf)
> +{
> +       struct sram_dma_heap_buffer *buffer = dmabuf->priv;
> +
> +       return buffer->vaddr;
> +}
> +
> +const struct dma_buf_ops sram_dma_heap_buf_ops = {
> +       .attach = dma_heap_attach,
> +       .detach = dma_heap_detatch,
> +       .map_dma_buf = dma_heap_map_dma_buf,
> +       .unmap_dma_buf = dma_heap_unmap_dma_buf,
> +       .release = dma_heap_dma_buf_release,
> +       .mmap = dma_heap_mmap,
> +       .vmap = dma_heap_vmap,
> +};

No begin/end_cpu_access functions here? I'm guessing it's because
you're always using SKIP_CPU_SYNC so it wouldn't do anything? A small
comment in the code might help.


> +
> +static int sram_dma_heap_allocate(struct dma_heap *heap,
> +                                 unsigned long len,
> +                                 unsigned long fd_flags,
> +                                 unsigned long heap_flags)
> +{
> +       struct sram_dma_heap *sram_dma_heap = dma_heap_get_drvdata(heap);
> +       struct sram_dma_heap_buffer *buffer;
> +
> +       DEFINE_DMA_BUF_EXPORT_INFO(exp_info);
> +       struct dma_buf *dmabuf;
> +       int ret;
> +
> +       buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
> +       if (!buffer)
> +               return -ENOMEM;
> +       buffer->pool = sram_dma_heap->pool;
> +       INIT_LIST_HEAD(&buffer->attachments);
> +       mutex_init(&buffer->attachments_lock);
> +       buffer->len = len;
> +
> +       buffer->vaddr = (void *)gen_pool_alloc(buffer->pool, buffer->len);
> +       if (!buffer->vaddr) {
> +               ret = -ENOMEM;
> +               goto free_buffer;
> +       }
> +
> +       buffer->paddr = gen_pool_virt_to_phys(buffer->pool, (unsigned long)buffer->vaddr);
> +       if (buffer->paddr == -1) {
> +               ret = -ENOMEM;
> +               goto free_pool;
> +       }
> +
> +       /* create the dmabuf */
> +       exp_info.ops = &sram_dma_heap_buf_ops;
> +       exp_info.size = buffer->len;
> +       exp_info.flags = fd_flags;
> +       exp_info.priv = buffer;
> +       dmabuf = dma_buf_export(&exp_info);
> +       if (IS_ERR(dmabuf)) {
> +               ret = PTR_ERR(dmabuf);
> +               goto free_pool;
> +       }
> +
> +       ret = dma_buf_fd(dmabuf, fd_flags);
> +       if (ret < 0) {
> +               dma_buf_put(dmabuf);
> +               /* just return, as put will call release and that will free */
> +               return ret;
> +       }
> +
> +       return ret;
> +
> +free_pool:
> +       gen_pool_free(buffer->pool, (unsigned long)buffer->vaddr, buffer->len);
> +free_buffer:
> +       kfree(buffer);
> +
> +       return ret;
> +}
> +
> +static struct dma_heap_ops sram_dma_heap_ops = {
> +       .allocate = sram_dma_heap_allocate,
> +};
> +
> +int sram_dma_heap_export(struct sram_dev *sram,

This is totally a bikeshed thing (feel free to ignore), but maybe
sram_dma_heap_create()  or _add() would be a better name to avoid
folks mixing it up with the dmabuf exporter?

> +                        struct sram_reserve *block,
> +                        phys_addr_t start,
> +                        struct sram_partition *part)
> +{
> +       struct sram_dma_heap *sram_dma_heap;
> +       struct dma_heap_export_info exp_info;
> +
> +       dev_info(sram->dev, "Exporting SRAM pool '%s'\n", block->label);

Again, shed issue: but for terminology consistency (at least in the
dmabuf heaps space), maybe heap instead of pool?

Thanks so much again for submitting this!
-john