[PATCH 02/13] media: rockchip: rga: extract helper to fill descriptors

[Michael Tretter]

Hi Robin,

On Thu, 14 Sep 2023 16:06:27 +0100, Robin Murphy wrote:
> On 2023-09-14 13:40, Michael Tretter wrote:
> > The IOMMU of the RGA is programmed with a list of DMA descriptors that
> > contain an 32 bit address per 4k page in the video buffers. The address
> > in the descriptor points to the start address of the page.
> > 
> > Introduce 'struct rga_dma_desc' to make the handling of the DMA
> > descriptors explicit instead of hiding them behind standard types.
> > 
> > As the descriptors only handle 32 bit addresses, addresses above 4 GB
> > cannot be addressed. If this is detected, stop filling the descriptor
> > list and report an error.
> 
> That sounds unnecessary, since the only DMA addresses the RGA should be
> seeing are those from a dma_map_sg() call using the RGA device itself, and
> that would have failed if it was unable to provide a valid DMA address for
> the device.
> 
> The existing rga_buf_map() code is so clearly wrong I can't tell whether
> that mapping is done somewhere out in the core framework or whether the
> driver's supposed to be doing it for itself.

The sg_table is filled by dma_map_sgtable in
drivers/media/common/videobuf2/videobuf2-dma-sg.c.

Do you suggest to just drop the check for the addresses or is there something
fundamentally wrong with filling the descriptor list in the driver? Can you
explain what exactly is wrong with this code and do you have a pointer how to
implement this correctly?

Thanks,

Michael

> 
> Thanks,
> Robin.
> 
> > While at it, use provided helpers for iterating the sg_table instead of
> > manually calculating the DMA addresses.
> > 
> > Signed-off-by: Michael Tretter <m.tretter at pengutronix.de>
> > ---
> >   drivers/media/platform/rockchip/rga/rga-buf.c | 47 +++++++++++++++------------
> >   drivers/media/platform/rockchip/rga/rga.h     |  8 +++--
> >   2 files changed, 33 insertions(+), 22 deletions(-)
> > 
> > diff --git a/drivers/media/platform/rockchip/rga/rga-buf.c b/drivers/media/platform/rockchip/rga/rga-buf.c
> > index 81508ed5abf3..df5ebc90e32d 100644
> > --- a/drivers/media/platform/rockchip/rga/rga-buf.c
> > +++ b/drivers/media/platform/rockchip/rga/rga-buf.c
> > @@ -5,6 +5,7 @@
> >    */
> >   #include <linux/pm_runtime.h>
> > +#include <linux/scatterlist.h>
> >   #include <media/v4l2-device.h>
> >   #include <media/v4l2-ioctl.h>
> > @@ -15,6 +16,25 @@
> >   #include "rga-hw.h"
> >   #include "rga.h"
> > +static int fill_descriptors(struct rga_dma_desc *desc, struct sg_table *sgt)
> > +{
> > +	struct sg_dma_page_iter iter;
> > +	struct rga_dma_desc *tmp = desc;
> > +	unsigned int num_desc = 0;
> > +	dma_addr_t addr;
> > +
> > +	for_each_sgtable_dma_page(sgt, &iter, 0) {
> > +		addr = sg_page_iter_dma_address(&iter);
> > +		if (upper_32_bits(addr) != 0L)
> > +			return -1;
> > +		tmp->addr = lower_32_bits(addr);
> > +		tmp++;
> > +		num_desc++;
> > +	}
> > +
> > +	return num_desc;
> > +}
> > +
> >   static int
> >   rga_queue_setup(struct vb2_queue *vq,
> >   		unsigned int *nbuffers, unsigned int *nplanes,
> > @@ -114,11 +134,8 @@ void rga_buf_map(struct vb2_buffer *vb)
> >   {
> >   	struct rga_ctx *ctx = vb2_get_drv_priv(vb->vb2_queue);
> >   	struct rockchip_rga *rga = ctx->rga;
> > -	struct sg_table *sgt;
> > -	struct scatterlist *sgl;
> > -	unsigned int *pages;
> > -	unsigned int address, len, i, p;
> > -	unsigned int mapped_size = 0;
> > +	struct rga_dma_desc *pages;
> > +	unsigned int num_desc = 0;
> >   	if (vb->type == V4L2_BUF_TYPE_VIDEO_OUTPUT)
> >   		pages = rga->src_mmu_pages;
> > @@ -126,23 +143,13 @@ void rga_buf_map(struct vb2_buffer *vb)
> >   		pages = rga->dst_mmu_pages;
> >   	/* Create local MMU table for RGA */
> > -	sgt = vb2_plane_cookie(vb, 0);
> > -
> > -	for_each_sg(sgt->sgl, sgl, sgt->nents, i) {
> > -		len = sg_dma_len(sgl) >> PAGE_SHIFT;
> > -		address = sg_phys(sgl);
> > -
> > -		for (p = 0; p < len; p++) {
> > -			dma_addr_t phys = address +
> > -					  ((dma_addr_t)p << PAGE_SHIFT);
> > -
> > -			pages[mapped_size + p] = phys;
> > -		}
> > -
> > -		mapped_size += len;
> > +	num_desc = fill_descriptors(pages, vb2_dma_sg_plane_desc(vb, 0));
> > +	if (num_desc < 0) {
> > +		dev_err(rga->dev, "Failed to map buffer");
> > +		return;
> >   	}
> >   	/* sync local MMU table for RGA */
> >   	dma_sync_single_for_device(rga->dev, virt_to_phys(pages),
> > -				   8 * PAGE_SIZE, DMA_BIDIRECTIONAL);
> > +				   num_desc * sizeof(*pages), DMA_BIDIRECTIONAL);
> >   }
> > diff --git a/drivers/media/platform/rockchip/rga/rga.h b/drivers/media/platform/rockchip/rga/rga.h
> > index 5fa9d2f366dc..22f7da28ac51 100644
> > --- a/drivers/media/platform/rockchip/rga/rga.h
> > +++ b/drivers/media/platform/rockchip/rga/rga.h
> > @@ -40,6 +40,10 @@ struct rga_frame {
> >   	u32 size;
> >   };
> > +struct rga_dma_desc {
> > +	u32 addr;
> > +};
> > +
> >   struct rockchip_rga_version {
> >   	u32 major;
> >   	u32 minor;
> > @@ -81,8 +85,8 @@ struct rockchip_rga {
> >   	struct rga_ctx *curr;
> >   	dma_addr_t cmdbuf_phy;
> >   	void *cmdbuf_virt;
> > -	unsigned int *src_mmu_pages;
> > -	unsigned int *dst_mmu_pages;
> > +	struct rga_dma_desc *src_mmu_pages;
> > +	struct rga_dma_desc *dst_mmu_pages;
> >   };
> >   struct rga_frame *rga_get_frame(struct rga_ctx *ctx, enum v4l2_buf_type type);
> > 
>