On Wed, 15 Oct 2025, Gustavo Sousa <[email protected]> wrote:
> From: Sai Teja Pottumuttu <[email protected]>
>
> Currently there is no way in the driver to classify the underruns into
> different categories. Starting with Xe3p_LPD, we get two new registers
> and some bits in existing registers which can help us categorise the
> underruns and let us know possible reason behind the underrun.
>
> Bspec: 69111, 69561, 74411, 74412
> Signed-off-by: Sai Teja Pottumuttu <[email protected]>
> Signed-off-by: Gustavo Sousa <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_display_regs.h | 31 +++++++
> drivers/gpu/drm/i915/display/intel_fifo_underrun.c | 100
> ++++++++++++++++++++-
> 2 files changed, 130 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display_regs.h
> b/drivers/gpu/drm/i915/display/intel_display_regs.h
> index 9d71e26a4fa2..9e2414b730db 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_regs.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_regs.h
> @@ -882,6 +882,36 @@
> #define PIPE_MISC2_FLIP_INFO_PLANE_SEL_MASK REG_GENMASK(2,
> 0) /* tgl+ */
> #define PIPE_MISC2_FLIP_INFO_PLANE_SEL(plane_id)
> REG_FIELD_PREP(PIPE_MISC2_FLIP_INFO_PLANE_SEL_MASK, (plane_id))
>
> +#define _UNDERRUN_DBG1_A 0x70064
> +#define _UNDERRUN_DBG1_B 0x71064
> +#define UNDERRUN_DBG1(pipe) _MMIO_PIPE(pipe, \
> +
> _UNDERRUN_DBG1_A, \
> +
> _UNDERRUN_DBG1_B)
> +#define UNDERRUN_DBUF_BLOCK_NOT_VALID_MASK REG_GENMASK(29, 24)
> +#define UNDERRUN_DBUF_BLOCK_NOT_VALID_PLANE_CURSOR REG_BIT(24)
> +#define UNDERRUN_DDB_EMPTY_MASK REG_GENMASK(21, 16)
> +#define UNDERRUN_DDB_EMPTY_PLANE_CURSOR REG_BIT(16)
> +#define UNDERRUN_DBUF_NOT_FILLED_MASK REG_GENMASK(13,
> 8)
> +#define UNDERRUN_DBUF_NOT_FILLED_PLANE_CURSOR REG_BIT(8)
> +#define UNDERRUN_BELOW_WM0_MASK REG_GENMASK(5, 0)
> +#define UNDERRUN_BELOW_WM0_PLANE_CURSOR REG_BIT(0)
> +
> +#define _UNDERRUN_DBG2_A 0x70068
> +#define _UNDERRUN_DBG2_B 0x71068
> +#define UNDERRUN_DBG2(pipe) _MMIO_PIPE(pipe, \
> +
> _UNDERRUN_DBG2_A, \
> +
> _UNDERRUN_DBG2_B)
> +#define UNDERRUN_FRAME_LINE_COUNTERS_FROZEN REG_BIT(31)
> +#define UNDERRUN_PIPE_FRAME_COUNT_MASK REG_GENMASK(30, 20)
> +#define UNDERRUN_LINE_COUNT_MASK REG_GENMASK(19, 0)
> +
> +#define _FBC_DEBUG_STATUS_A 0x43220
> +#define _FBC_DEBUG_STATUS_B 0x43260
> +#define FBC_DEBUG_STATUS(pipe)
> _MMIO_PIPE(pipe, \
> +
> _FBC_DEBUG_STATUS_A, \
> +
> _FBC_DEBUG_STATUS_B)
> +#define FBC_UNDERRUN_DECOMPRESSION REG_BIT(27)
> +
> #define DPINVGTT _MMIO(VLV_DISPLAY_BASE +
> 0x7002c) /* VLV/CHV only */
> #define DPINVGTT_EN_MASK_CHV REG_GENMASK(27,
> 16)
> #define DPINVGTT_EN_MASK_VLV REG_GENMASK(23,
> 16)
> @@ -1416,6 +1446,7 @@
>
> #define GEN12_DCPR_STATUS_1 _MMIO(0x46440)
> #define XELPDP_PMDEMAND_INFLIGHT_STATUS REG_BIT(26)
> +#define XE3P_UNDERRUN_PKGC REG_BIT(21)
>
> #define FUSE_STRAP _MMIO(0x42014)
> #define ILK_INTERNAL_GRAPHICS_DISABLE REG_BIT(31)
> diff --git a/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
> b/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
> index c2ce8461ac9e..753872ad28ed 100644
> --- a/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
> +++ b/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
> @@ -352,6 +352,101 @@ bool intel_set_pch_fifo_underrun_reporting(struct
> intel_display *display,
> return old;
> }
>
> +static void snprintf_underrun_planes(char *buf, size_t len,
> + u32 underrun_dbg, u32 underrun_cursor)
> +{
> + snprintf(buf, len, "%s%s%s%s%s%s",
> + underrun_dbg & (underrun_cursor << 1) ? "[1]" : "",
> + underrun_dbg & (underrun_cursor << 2) ? "[2]" : "",
> + underrun_dbg & (underrun_cursor << 3) ? "[3]" : "",
> + underrun_dbg & (underrun_cursor << 4) ? "[4]" : "",
> + underrun_dbg & (underrun_cursor << 5) ? "[5]" : "",
> + underrun_dbg & underrun_cursor ? "[C]" : "");
> +}
I'm pretty sure this could be made cleaner by using seq_buf.
> +
> +static void xe3p_lpd_log_underrun(struct intel_display *display,
> + enum pipe pipe)
> +{
> + u32 underrun_dbg1;
> + u32 underrun_dbg2;
> + u32 fbc_debug_status;
> + u32 dcpr_status;
> + char planes[32];
> +
> + /*
> + * UNDERRUN_DBG1 reports the following things
> + * 1. If DBUF block is not valid
> + * 2. If DDB is empty
> + * 3. If streamer could not completely fill DBUF at the end of vblank
> + * 4. Each enabled plane/cursor below watermark 0
> + */
> + underrun_dbg1 = intel_de_read(display, UNDERRUN_DBG1(pipe));
> + intel_de_write(display, UNDERRUN_DBG1(pipe), underrun_dbg1);
> +
> + if (underrun_dbg1 & UNDERRUN_DBUF_BLOCK_NOT_VALID_MASK) {
> + snprintf_underrun_planes(planes, sizeof(planes), underrun_dbg1,
> +
> UNDERRUN_DBUF_BLOCK_NOT_VALID_PLANE_CURSOR);
> + drm_err(display->drm,
> + "Pipe %c FIFO underrun: DBUF block not valid for
> plane(s): %s\n",
> + pipe_name(pipe), planes);
> + }
> +
> + if (underrun_dbg1 & UNDERRUN_DDB_EMPTY_MASK) {
> + snprintf_underrun_planes(planes, sizeof(planes), underrun_dbg1,
> + UNDERRUN_DDB_EMPTY_PLANE_CURSOR);
> + drm_err(display->drm, "Pipe %c FIFO underrun: DDB empty for
> plane(s): %s\n",
> + pipe_name(pipe), planes);
> + }
> +
> + if (underrun_dbg1 & UNDERRUN_DBUF_NOT_FILLED_MASK) {
> + snprintf_underrun_planes(planes, sizeof(planes), underrun_dbg1,
> + UNDERRUN_DBUF_NOT_FILLED_PLANE_CURSOR);
> + drm_err(display->drm, "Pipe %c FIFO underrun: DBUF not filled
> for plane(s): %s\n",
> + pipe_name(pipe), planes);
> + }
> +
> + if (underrun_dbg1 & UNDERRUN_BELOW_WM0_MASK) {
> + snprintf_underrun_planes(planes, sizeof(planes), underrun_dbg1,
> + UNDERRUN_BELOW_WM0_PLANE_CURSOR);
> + drm_err(display->drm, "Pipe %c FIFO underrun: Below watermark 0
> on plane(s): %s\n",
> + pipe_name(pipe), planes);
> + }
> +
> + /*
> + * UNDERRUN_DBG2 reports the frame count and line count when the
> underrun started.
> + */
> + underrun_dbg2 = intel_de_read(display, UNDERRUN_DBG2(pipe));
> + if (underrun_dbg2 & UNDERRUN_FRAME_LINE_COUNTERS_FROZEN) {
> + intel_de_write(display, UNDERRUN_DBG2(pipe),
> UNDERRUN_FRAME_LINE_COUNTERS_FROZEN);
> + drm_err(display->drm, "Pipe %c FIFO underrun: Frame count: %u,
> Line count: %u\n",
> + pipe_name(pipe),
> + REG_FIELD_GET(UNDERRUN_PIPE_FRAME_COUNT_MASK,
> underrun_dbg2),
> + REG_FIELD_GET(UNDERRUN_LINE_COUNT_MASK, underrun_dbg2));
> + }
> +
> + /*
> + * FBC_DEBUG_STATUS's FBC_UNDERRUN_DECOMPRESSION indicates if FBC was
> + * decompressing when underrun got triggered.
> + */
> + fbc_debug_status = intel_de_read(display, FBC_DEBUG_STATUS(pipe));
> + if (fbc_debug_status & FBC_UNDERRUN_DECOMPRESSION) {
> + intel_de_write(display, FBC_DEBUG_STATUS(pipe),
> FBC_UNDERRUN_DECOMPRESSION);
> + drm_err(display->drm, "Pipe %c FIFO underrun: FBC
> decompression\n",
> + pipe_name(pipe));
> + }
> +
> + /*
> + * GEN12_DCPR_STATUS_1's XE3P_UNDERRUN_PKGC, indicates that underrun
> started
> + * while pkgc was blocking memory.
> + */
> + dcpr_status = intel_de_read(display, GEN12_DCPR_STATUS_1);
> + if (dcpr_status & XE3P_UNDERRUN_PKGC) {
> + intel_de_write(display, GEN12_DCPR_STATUS_1,
> XE3P_UNDERRUN_PKGC);
> + drm_err(display->drm, "Pipe %c FIFO underrun: Pkgc blocking
> memory\n",
> + pipe_name(pipe));
> + }
> +}
> +
> /**
> * intel_cpu_fifo_underrun_irq_handler - handle CPU fifo underrun interrupt
> * @display: display device instance
> @@ -378,7 +473,10 @@ void intel_cpu_fifo_underrun_irq_handler(struct
> intel_display *display,
> if (intel_set_cpu_fifo_underrun_reporting(display, pipe, false)) {
> trace_intel_cpu_fifo_underrun(display, pipe);
>
> - drm_err(display->drm, "CPU pipe %c FIFO underrun\n",
> pipe_name(pipe));
> + if (DISPLAY_VER(display) >= 35)
> + xe3p_lpd_log_underrun(display, pipe);
> + else
> + drm_err(display->drm, "CPU pipe %c FIFO underrun\n",
> pipe_name(pipe));
> }
>
> intel_fbc_handle_fifo_underrun_irq(display);
--
Jani Nikula, Intel
