[PATCH 4/4] drm/mgag200: Use DMA to copy the framebuffer to the VRAM
Thomas Zimmermann
tzimmermann at suse.de
Mon May 8 08:04:32 UTC 2023
Hi Jocelyn
Am 05.05.23 um 14:43 schrieb Jocelyn Falempe:
> Even if the transfer is not faster, it brings significant
> improvement in latencies and CPU usage.
>
I think I shot down this patch already. I don't want to maintain the
extra code for DMA support.
> CPU usage drops from 100% of one core to 3% when continuously
> refreshing the screen.
But this result is nice, so mabe I'd reconsider. Let's take this patch
as an RFC to discuss possible ways forward.
There seems to be some fallback still in place in this patch. I
definately don't want multiple codepaths for copying; so the DMA code
needs to work on all our hardware.
>
> The primary DMA is used to send commands (register write), and
> the secondary DMA to send the pixel data.
> It uses the ILOAD command (chapter 4.5.7 in G200 specification),
> which allows to load an image, or a part of an image from system
> memory to VRAM.
> The last command sent, is a softrap command, which triggers an IRQ
> when the DMA transfer is complete.
> For 16bits and 24bits pixel width, each line is padded to make sure,
> the DMA transfer is a multiple of 32bits. The padded bytes won't be
> drawn on the screen, so they don't need to be initialized.
>
> Signed-off-by: Jocelyn Falempe <jfalempe at redhat.com>
> ---
> drivers/gpu/drm/mgag200/Makefile | 3 +-
> drivers/gpu/drm/mgag200/mgag200_dma.c | 114 +++++++++++++++++++++
> drivers/gpu/drm/mgag200/mgag200_drv.c | 2 +
> drivers/gpu/drm/mgag200/mgag200_drv.h | 25 +++++
> drivers/gpu/drm/mgag200/mgag200_mode.c | 131 ++++++++++++++++++++++++-
> drivers/gpu/drm/mgag200/mgag200_reg.h | 25 +++++
> 6 files changed, 295 insertions(+), 5 deletions(-)
> create mode 100644 drivers/gpu/drm/mgag200/mgag200_dma.c
>
> diff --git a/drivers/gpu/drm/mgag200/Makefile b/drivers/gpu/drm/mgag200/Makefile
> index 182e224c460d..96e23dc5572c 100644
> --- a/drivers/gpu/drm/mgag200/Makefile
> +++ b/drivers/gpu/drm/mgag200/Makefile
> @@ -11,6 +11,7 @@ mgag200-y := \
> mgag200_g200se.o \
> mgag200_g200wb.o \
> mgag200_i2c.o \
> - mgag200_mode.o
> + mgag200_mode.o \
> + mgag200_dma.o
>
> obj-$(CONFIG_DRM_MGAG200) += mgag200.o
> diff --git a/drivers/gpu/drm/mgag200/mgag200_dma.c b/drivers/gpu/drm/mgag200/mgag200_dma.c
> new file mode 100644
> index 000000000000..fe063fa2b5f1
> --- /dev/null
> +++ b/drivers/gpu/drm/mgag200/mgag200_dma.c
> @@ -0,0 +1,114 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright 2023 Red Hat
> + *
> + * Authors: Jocelyn Falempe
> + *
> + */
> +
> +#include <linux/wait.h>
> +#include <linux/dma-mapping.h>
> +
> +#include "mgag200_drv.h"
> +#include "mgag200_reg.h"
> +
> +/* Maximum number of command block for one DMA transfert
> + * iload should only use 4 blocks
> + */
> +#define MGA_MAX_CMD 50
> +
> +#define MGA_DMA_SIZE (4 * 1024 * 1024)
> +#define MGA_MIN_DMA_SIZE (64 * 1024)
> +
> +/*
> + * Allocate coherent buffers for DMA transfert.
> + * We need two buffers, one for the commands, and one for the data.
> + * If allocation fails, mdev->dma_buf will be NULL, and the driver will
> + * fallback to memcpy().
> + */
> +void mgag200_dma_allocate(struct mga_device *mdev)
> +{
> + struct drm_device *dev = &mdev->base;
> + int size;
> + /* Allocate the command buffer */
> + mdev->cmd = dmam_alloc_coherent(dev->dev, MGA_MAX_CMD * sizeof(*mdev->cmd),
> + &mdev->cmd_handle, GFP_KERNEL);
> +
> + if (!mdev->cmd) {
> + drm_warn(dev, "DMA command buffer allocation failed, fallback to cpu copy\n");
> + return;
> + }
> +
> + for (size = MGA_DMA_SIZE; size >= MGA_MIN_DMA_SIZE; size = size >> 1) {
> + mdev->dma_buf = dmam_alloc_coherent(dev->dev, size, &mdev->dma_handle, GFP_KERNEL);
> + if (mdev->dma_buf)
> + break;
> + }
> + if (!mdev->dma_buf) {
> + drm_warn(dev, "DMA data buffer allocation failed, fallback to cpu copy\n");
> + return;
> + }
> + mdev->dma_size = size;
> + drm_info(dev, "Using DMA with a %dk data buffer\n", size / 1024);
> +}
> +
> +/*
> + * Matrox uses commands block to program the hardware through DMA.
> + * Each command is a register write, and each block contains 4 commands
> + * packed in 5 words(u32).
> + * First word is the 4 register index (8bit) to write for the 4 commands,
> + * followed by the four values to be written.
> + */
> +void mgag200_dma_add_block(struct mga_device *mdev,
> + u32 reg0, u32 val0,
> + u32 reg1, u32 val1,
> + u32 reg2, u32 val2,
> + u32 reg3, u32 val3)
> +{
> + if (mdev->cmd_idx >= MGA_MAX_CMD) {
> + pr_err("mgag200: exceeding the DMA command buffer size\n");
> + return;
> + }
> +
> + mdev->cmd[mdev->cmd_idx] = (struct mga_cmd_block) {
> + .cmd = DMAREG(reg0) | DMAREG(reg1) << 8 | DMAREG(reg2) << 16 | DMAREG(reg3) << 24,
> + .v0 = val0,
> + .v1 = val1,
> + .v2 = val2,
> + .v3 = val3};
> + mdev->cmd_idx++;
> +}
> +
> +void mgag200_dma_run_cmd(struct mga_device *mdev)
> +{
> + struct drm_device *dev = &mdev->base;
> + u32 primend;
> + int ret;
> +
> + /* Add a last block to trigger the softrap interrupt */
> + mgag200_dma_add_block(mdev,
> + MGAREG_DMAPAD, 0,
> + MGAREG_DMAPAD, 0,
> + MGAREG_DMAPAD, 0,
> + MGAREG_SOFTRAP, 0);
> +
> + primend = mdev->cmd_handle + mdev->cmd_idx * sizeof(struct mga_cmd_block);
> +
> + // Use primary DMA to send the commands
> + WREG32(MGAREG_PRIMADDR, (u32) mdev->cmd_handle);
> + WREG32(MGAREG_PRIMEND, primend);
> + mdev->dma_in_use = 1;
> +
> + ret = wait_event_timeout(mdev->waitq, mdev->dma_in_use == 0, HZ);
> +
> + if (mdev->dma_in_use) {
> + drm_err(dev, "DMA transfert timed out\n");
> + /* something goes wrong, reset the DMA engine */
> + WREG8(MGAREG_OPMODE, MGAOPM_DMA_BLIT);
> + mdev->dma_in_use = 0;
> + }
> +
> + /* reset command index to start a new sequence */
> + mdev->cmd_idx = 0;
> +}
Can the DMA code be build around Linux' struct drm_device?
> +
> diff --git a/drivers/gpu/drm/mgag200/mgag200_drv.c b/drivers/gpu/drm/mgag200/mgag200_drv.c
> index 3566fcdfe1e4..c863487526e7 100644
> --- a/drivers/gpu/drm/mgag200/mgag200_drv.c
> +++ b/drivers/gpu/drm/mgag200/mgag200_drv.c
> @@ -184,6 +184,8 @@ int mgag200_device_preinit(struct mga_device *mdev)
> if (!mdev->vram)
> return -ENOMEM;
>
> + mgag200_dma_allocate(mdev);
> +
> mgag200_init_irq(mdev);
> ret = devm_request_irq(dev->dev, pdev->irq, mgag200_driver_irq_handler,
> IRQF_SHARED, "mgag200_irq", mdev);
> diff --git a/drivers/gpu/drm/mgag200/mgag200_drv.h b/drivers/gpu/drm/mgag200/mgag200_drv.h
> index 02175bfaf5a8..f5060fdc16f9 100644
> --- a/drivers/gpu/drm/mgag200/mgag200_drv.h
> +++ b/drivers/gpu/drm/mgag200/mgag200_drv.h
> @@ -277,6 +277,14 @@ struct mgag200_device_funcs {
> void (*pixpllc_atomic_update)(struct drm_crtc *crtc, struct drm_atomic_state *old_state);
> };
>
> +struct mga_cmd_block {
> + u32 cmd;
> + u32 v0;
> + u32 v1;
> + u32 v2;
> + u32 v3;
> +} __packed;
> +
> struct mga_device {
> struct drm_device base;
>
> @@ -291,6 +299,14 @@ struct mga_device {
> void __iomem *vram;
> resource_size_t vram_available;
>
> + void *dma_buf;
> + size_t dma_size;
> + dma_addr_t dma_handle;
> +
> + struct mga_cmd_block *cmd;
> + int cmd_idx;
> + dma_addr_t cmd_handle;
> +
> wait_queue_head_t waitq;
> int dma_in_use;
>
> @@ -446,4 +462,13 @@ void mgag200_bmc_enable_vidrst(struct mga_device *mdev);
> /* mgag200_i2c.c */
> int mgag200_i2c_init(struct mga_device *mdev, struct mga_i2c_chan *i2c);
>
> +/* mgag200_dma.c */
> +void mgag200_dma_allocate(struct mga_device *mdev);
> +void mgag200_dma_add_block(struct mga_device *mdev,
> + u32 reg0, u32 val0,
> + u32 reg1, u32 val1,
> + u32 reg2, u32 val2,
> + u32 reg3, u32 val3);
> +void mgag200_dma_run_cmd(struct mga_device *mdev);
> +
> #endif /* __MGAG200_DRV_H__ */
> diff --git a/drivers/gpu/drm/mgag200/mgag200_mode.c b/drivers/gpu/drm/mgag200/mgag200_mode.c
> index 7d8c65372ac4..7825ec4323d2 100644
> --- a/drivers/gpu/drm/mgag200/mgag200_mode.c
> +++ b/drivers/gpu/drm/mgag200/mgag200_mode.c
> @@ -398,13 +398,132 @@ static void mgag200_disable_display(struct mga_device *mdev)
> WREG_ECRT(0x01, crtcext1);
> }
>
> +static void mgag200_dwg_setup(struct mga_device *mdev, struct drm_framebuffer *fb)
> +{
> + u32 maccess;
> +
> + drm_dbg(&mdev->base, "Setup DWG with %dx%d %p4cc\n",
> + fb->width, fb->height, &fb->format->format);
> +
> + switch (fb->format->format) {
> + case DRM_FORMAT_RGB565:
> + maccess = MGAMAC_PW16;
> + break;
> + case DRM_FORMAT_RGB888:
> + maccess = MGAMAC_PW24;
> + break;
> + case DRM_FORMAT_XRGB8888:
> + maccess = MGAMAC_PW32;
> + break;
> + }
> + WREG32(MGAREG_MACCESS, maccess);
> +
> + /* Framebuffer width in pixel */
> + WREG32(MGAREG_PITCH, fb->width);
> +
> + /* Sane default value for the drawing engine registers */
> + WREG32(MGAREG_DSTORG, 0);
> + WREG32(MGAREG_YDSTORG, 0);
> + WREG32(MGAREG_SRCORG, 0);
> + WREG32(MGAREG_CXBNDRY, 0x0FFF0000);
> + WREG32(MGAREG_YTOP, 0);
> + WREG32(MGAREG_YBOT, 0x00FFFFFF);
> +
> + /* Activate blit mode DMA, only write the low part of the register */
> + WREG8(MGAREG_OPMODE, MGAOPM_DMA_BLIT);
> +}
> +
> +/*
> + * ILOAD allows to load an image from system memory to the VRAM, and with FXBNDRY, YDST and YDSTLEN,
> + * you can transfert a rectangle, so it's perfect when used with a damage clip.
> + */
> +static void mgag200_iload_cmd(struct mga_device *mdev, int x, int y, int width, int height,
> + int width_padded, int cpp)
> +{
> + int size = width_padded * height;
> + u32 iload;
> +
> + iload = MGADWG_ILOAD | MGADWG_SGNZERO | MGADWG_SHIFTZERO | MGADWG_REPLACE | MGADWG_CLIPDIS
> + | MGADWG_BFCOL;
> +
> + mgag200_dma_add_block(mdev,
> + MGAREG_DWGCTL, iload,
> + MGAREG_FXBNDRY, (((x + width - 1) << 16) | x),
> + MGAREG_AR0, (width_padded / cpp) - 1,
> + MGAREG_AR3, 0);
> +
> + mgag200_dma_add_block(mdev,
> + MGAREG_AR5, 0,
> + MGAREG_YDST, y,
> + MGAREG_DMAPAD, 0,
> + MGAREG_DMAPAD, 0);
> +
> + mgag200_dma_add_block(mdev,
> + MGAREG_DMAPAD, 0,
> + MGAREG_LEN | MGAREG_EXEC, height,
> + MGAREG_SECADDR, mdev->dma_handle | 1,
> + /* Writing SECEND should always be the last command of a block */
> + MGAREG_SECEND, mdev->dma_handle + size);
> +}
> +
> +static void mgag200_dma_copy(struct mga_device *mdev, const void *src, u32 pitch,
> + struct drm_rect *clip, int cpp)
> +{
> + int i;
> + int width = drm_rect_width(clip);
> + int height = drm_rect_height(clip);
> +
> + /* pad each line to 32bits boundaries see section 4.5.7 of G200 Specification */
> + int width_padded = round_up(width * cpp, 4);
> +
> + for (i = 0; i < height; i++)
> + memcpy(mdev->dma_buf + width_padded * i,
> + src + (((clip->y1 + i) * pitch) + clip->x1 * cpp),
> + width * cpp);
This memcpy() should probably go away. Instead of SHMEM, mgag200 should
allocate with GEM DMA helpers. We have a number of drivers that use DMA
helpers with DRM format helpers, so the conversion should be
strait-forward and can be done independently from the other patches.
Afterward, it should be possible to DMA-copy directly from the GEM
buffer object.
> +
> + mgag200_iload_cmd(mdev, clip->x1, clip->y1, width, height, width_padded, cpp);
> + mgag200_dma_run_cmd(mdev);
> +}
> +
> +/*
> + * If the DMA coherent buffer is smaller than damage rectangle, we need to
> + * split it into multiple DMA transfert.
> + */
> +static void mgag200_dma_damage(struct mga_device *mdev, const struct iosys_map *vmap,
> + struct drm_framebuffer *fb, struct drm_rect *clip)
> +{
> + u32 pitch = fb->pitches[0];
> + const void *src = vmap[0].vaddr;
> + struct drm_rect subclip;
> + int y1;
> + int lines;
> + int cpp = fb->format->cpp[0];
> +
> + /* Number of lines that fits in one DMA buffer */
> + lines = min(drm_rect_height(clip), (int) mdev->dma_size / (drm_rect_width(clip) * cpp));
> +
> + subclip.x1 = clip->x1;
> + subclip.x2 = clip->x2;
> +
> + for (y1 = clip->y1; y1 < clip->y2; y1 += lines) {
> + subclip.y1 = y1;
> + subclip.y2 = min(clip->y2, y1 + lines);
> + mgag200_dma_copy(mdev, src, pitch, &subclip, cpp);
> + }
> +}
> +
> static void mgag200_handle_damage(struct mga_device *mdev, const struct iosys_map *vmap,
> struct drm_framebuffer *fb, struct drm_rect *clip)
> {
> - struct iosys_map dst = IOSYS_MAP_INIT_VADDR_IOMEM(mdev->vram);
> -
> - iosys_map_incr(&dst, drm_fb_clip_offset(fb->pitches[0], fb->format, clip));
> - drm_fb_memcpy(&dst, fb->pitches, vmap, fb, clip);
> + if (mdev->dma_buf) {
> + /* Fast path, use DMA */
> + mgag200_dma_damage(mdev, vmap, fb, clip);
> + } else {
> + struct iosys_map dst = IOSYS_MAP_INIT_VADDR_IOMEM(mdev->vram);
> +
> + iosys_map_incr(&dst, drm_fb_clip_offset(fb->pitches[0], fb->format, clip));
> + drm_fb_memcpy(&dst, fb->pitches, vmap, fb, clip);
> + }
This branching needs to go. As I said, DMA is either the standard, or
not there at all. I doubt that the !mdev->dmabuf case can easily happen
in practice. AFAICT it's all in the 32-bit address range and we're on
systems with enough physical memory.
Best regards
Thomas
> }
>
> /*
> @@ -475,6 +594,10 @@ void mgag200_primary_plane_helper_atomic_update(struct drm_plane *plane,
> if (!fb)
> return;
>
> + if (!old_plane_state->fb || fb->format != old_plane_state->fb->format
> + || fb->width != old_plane_state->fb->width)
> + mgag200_dwg_setup(mdev, fb);
> +
> drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
> drm_atomic_for_each_plane_damage(&iter, &damage) {
> mgag200_handle_damage(mdev, shadow_plane_state->data, fb, &damage);
> diff --git a/drivers/gpu/drm/mgag200/mgag200_reg.h b/drivers/gpu/drm/mgag200/mgag200_reg.h
> index 748c8e18e938..256ac92dae56 100644
> --- a/drivers/gpu/drm/mgag200/mgag200_reg.h
> +++ b/drivers/gpu/drm/mgag200/mgag200_reg.h
> @@ -116,6 +116,9 @@
>
> #define MGAREG_OPMODE 0x1e54
>
> +#define MGAREG_PRIMADDR 0x1e58
> +#define MGAREG_PRIMEND 0x1e5c
> +
> /* Warp Registers */
> #define MGAREG_WIADDR 0x1dc0
> #define MGAREG_WIADDR2 0x1dd8
> @@ -200,6 +203,8 @@
>
> /* See table on 4-43 for bop ALU operations */
>
> +#define MGADWG_REPLACE (0xC << 16)
> +
> /* See table on 4-44 for translucidity masks */
>
> #define MGADWG_BMONOLEF ( 0x00 << 25 )
> @@ -218,6 +223,8 @@
>
> #define MGADWG_PATTERN ( 0x01 << 29 )
> #define MGADWG_TRANSC ( 0x01 << 30 )
> +#define MGADWG_CLIPDIS ( 0x01 << 31 )
> +
> #define MGAREG_MISC_WRITE 0x3c2
> #define MGAREG_MISC_READ 0x3cc
> #define MGAREG_MEM_MISC_WRITE 0x1fc2
> @@ -605,6 +612,9 @@
> # define MGA_TC2_SELECT_TMU1 (0x80000000)
> #define MGAREG_TEXTRANS 0x2c34
> #define MGAREG_TEXTRANSHIGH 0x2c38
> +#define MGAREG_SECADDR 0x2c40
> +#define MGAREG_SECEND 0x2c44
> +#define MGAREG_SOFTRAP 0x2c48
> #define MGAREG_TEXFILTER 0x2c58
> # define MGA_MIN_NRST (0x00000000)
> # define MGA_MIN_BILIN (0x00000002)
> @@ -691,4 +701,19 @@
> #define MGA_AGP2XPLL_ENABLE 0x1
> #define MGA_AGP2XPLL_DISABLE 0x0
>
> +
> +#define DWGREG0 0x1c00
> +#define DWGREG0_END 0x1dff
> +#define DWGREG1 0x2c00
> +#define DWGREG1_END 0x2dff
> +
> +/* These macros convert register address to the 8 bit command index used with DMA
> + * It remaps 0x1c00-0x1dff to 0x00-0x7f (REG0)
> + * and 0x2c00-0x2dff to 0x80-0xff (REG1)
> + */
> +#define ISREG0(r) (r >= DWGREG0 && r <= DWGREG0_END)
> +#define DMAREG0(r) ((u8)((r - DWGREG0) >> 2))
> +#define DMAREG1(r) ((u8)(((r - DWGREG1) >> 2) | 0x80))
> +#define DMAREG(r) (ISREG0((r)) ? DMAREG0((r)) : DMAREG1((r)))
> +
> #endif
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
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