On Fri, 07 Nov 2025, Gustavo Sousa <[email protected]> wrote:
> Xe3p_LPD added several bits containing information that can be relevant
> to debugging FIFO underruns. Add the logic necessary to handle them
> when reporting underruns.
>
> This was adapted from the initial patch[1] from Sai Teja Pottumuttu.
>
> [1]
> https://lore.kernel.org/all/[email protected]/
>
> Bspec: 69111, 69561, 74411, 74412
> Cc: Jani Nikula <[email protected]>
> Cc: Matt Roper <[email protected]>
> Cc: Ville Syrjälä <[email protected]>
> Signed-off-by: Gustavo Sousa <[email protected]>
> ---
> I tested this by adding a change on top of this series that updates
> Xe3p_LPD's CDCLK table to use bad values and I got the following
> messages:
>
> [ +0.000237] xe 0000:00:02.0: [drm:intel_modeset_verify_crtc [xe]]
> [CRTC:88:pipe A]
> [ +0.000674] xe 0000:00:02.0: [drm] *ERROR* CPU pipe A FIFO underrun
> [ +0.000015] xe 0000:00:02.0: [drm] *ERROR* Pipe A FIFO underrun info:
> DBUF block not valid on planes: [1]
> [ +0.000001] xe 0000:00:02.0: [drm] *ERROR* Pipe A FIFO underrun info:
> DDB empty on planes: [1]
> [ +0.000001] xe 0000:00:02.0: [drm] *ERROR* Pipe A FIFO underrun info:
> DBUF below WM0 on planes: [1]
> [ +0.000004] xe 0000:00:02.0: [drm] *ERROR* Pipe A FIFO underrun info:
> frame count: 1890, line count: 44
> ---
> .../gpu/drm/i915/display/intel_display_device.h | 1 +
> drivers/gpu/drm/i915/display/intel_display_regs.h | 16 +++
> drivers/gpu/drm/i915/display/intel_fbc_regs.h | 2 +
> drivers/gpu/drm/i915/display/intel_fifo_underrun.c | 128
> +++++++++++++++++++++
> 4 files changed, 147 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display_device.h
> b/drivers/gpu/drm/i915/display/intel_display_device.h
> index b559ef43d547..91d8cfac5eff 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_device.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_device.h
> @@ -197,6 +197,7 @@ struct intel_display_platforms {
> #define HAS_TRANSCODER(__display, trans)
> ((DISPLAY_RUNTIME_INFO(__display)->cpu_transcoder_mask & \
> BIT(trans)) != 0)
> #define HAS_UNCOMPRESSED_JOINER(__display) (DISPLAY_VER(__display) >= 13)
> +#define HAS_UNDERRUN_DBG_INFO(__display) (DISPLAY_VER(__display) >= 35)
> #define HAS_ULTRAJOINER(__display) (((__display)->platform.dgfx && \
> DISPLAY_VER(__display) == 14) &&
> HAS_DSC(__display))
> #define HAS_VRR(__display) (DISPLAY_VER(__display) >= 11)
> diff --git a/drivers/gpu/drm/i915/display/intel_display_regs.h
> b/drivers/gpu/drm/i915/display/intel_display_regs.h
> index 9d71e26a4fa2..89ea0156ee06 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_regs.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_regs.h
> @@ -882,6 +882,21 @@
> #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_DDB_EMPTY_MASK REG_GENMASK(21, 16)
> +#define UNDERRUN_DBUF_NOT_FILLED_MASK REG_GENMASK(13, 8)
> +#define UNDERRUN_BELOW_WM0_MASK REG_GENMASK(5, 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 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 +1431,7 @@
>
> #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_fbc_regs.h
> b/drivers/gpu/drm/i915/display/intel_fbc_regs.h
> index b1d0161a3196..77d8321c4fb3 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbc_regs.h
> +++ b/drivers/gpu/drm/i915/display/intel_fbc_regs.h
> @@ -88,6 +88,8 @@
> #define DPFC_FENCE_YOFF _MMIO(0x3218)
> #define ILK_DPFC_FENCE_YOFF(fbc_id) _MMIO_PIPE((fbc_id), 0x43218, 0x43258)
> #define DPFC_CHICKEN _MMIO(0x3224)
> +#define FBC_DEBUG_STATUS(fbc_id) _MMIO_PIPE((fbc_id), 0x43220, 0x43260)
> +#define FBC_UNDERRUN_DECMPR REG_BIT(27)
> #define ILK_DPFC_CHICKEN(fbc_id) _MMIO_PIPE((fbc_id), 0x43224, 0x43264)
> #define DPFC_HT_MODIFY REG_BIT(31) /* pre-ivb */
> #define DPFC_NUKE_ON_ANY_MODIFICATION REG_BIT(23) /* bdw+ */
> diff --git a/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
> b/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
> index c2ce8461ac9e..8a05b5c5fccd 100644
> --- a/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
> +++ b/drivers/gpu/drm/i915/display/intel_fifo_underrun.c
> @@ -25,6 +25,8 @@
> *
> */
>
> +#include <linux/seq_buf.h>
> +
> #include <drm/drm_print.h>
>
> #include "i915_reg.h"
> @@ -34,6 +36,7 @@
> #include "intel_display_trace.h"
> #include "intel_display_types.h"
> #include "intel_fbc.h"
> +#include "intel_fbc_regs.h"
> #include "intel_fifo_underrun.h"
> #include "intel_pch_display.h"
>
> @@ -57,6 +60,118 @@
> * The code also supports underrun detection on the PCH transcoder.
> */
>
> +#define UNDERRUN_DBG1_NUM_PLANES 6
> +
> +static void read_underrun_dbg1(struct intel_display *display, enum pipe
> pipe, bool log)
> +{
> + u32 val = intel_de_read(display, UNDERRUN_DBG1(pipe));
Nitpick, I really don't like the style of using "functional" (for want
of a better word) initializers. Complicated is fine, like below for
masks[], but doing something with the hardware or something that can
fail, feels iffy.
> + struct {
> + u32 plane_mask;
> + const char *info;
> + } masks[] = {
> + { REG_FIELD_GET(UNDERRUN_DBUF_BLOCK_NOT_VALID_MASK, val), "DBUF
> block not valid" },
> + { REG_FIELD_GET(UNDERRUN_DDB_EMPTY_MASK, val), "DDB empty" },
> + { REG_FIELD_GET(UNDERRUN_DBUF_NOT_FILLED_MASK, val), "DBUF not
> completely filled" },
> + { REG_FIELD_GET(UNDERRUN_BELOW_WM0_MASK, val), "DBUF below WM0"
> },
> + };
> + DECLARE_SEQ_BUF(planes_desc, 32);
> +
IMO there's also a lot more clarity in having the assignment and the
check back to back here:
val = intel_de_read(display, UNDERRUN_DBG1(pipe));
if (!val)
return;
Ditto below.
BR,
Jani.
> + if (!val)
> + return;
> +
> + intel_de_write(display, UNDERRUN_DBG1(pipe), val);
> +
> + if (!log)
> + return;
> +
> + for (int i = 0; i < ARRAY_SIZE(masks); i++) {
> + if (!masks[i].plane_mask)
> + continue;
> +
> + seq_buf_clear(&planes_desc);
> +
> + for (int j = 0; j < UNDERRUN_DBG1_NUM_PLANES; j++) {
> + if (!(masks[i].plane_mask & REG_BIT(j)))
> + continue;
> +
> + if (j == 0)
> + seq_buf_puts(&planes_desc, "[C]");
> + else
> + seq_buf_printf(&planes_desc, "[%d]", j);
> + }
> +
> + drm_err(display->drm,
> + "Pipe %c FIFO underrun info: %s on planes: %s\n",
> + pipe_name(pipe), masks[i].info,
> seq_buf_str(&planes_desc));
> +
> + drm_WARN_ON(display->drm, seq_buf_has_overflowed(&planes_desc));
> + }
> +}
> +
> +static void read_underrun_dbg2(struct intel_display *display, enum pipe
> pipe, bool log)
> +{
> + u32 val = intel_de_read(display, UNDERRUN_DBG2(pipe));
> +
> + if (!(val & UNDERRUN_FRAME_LINE_COUNTERS_FROZEN))
> + return;
> +
> + intel_de_write(display, UNDERRUN_DBG2(pipe),
> UNDERRUN_FRAME_LINE_COUNTERS_FROZEN);
> +
> + if (log)
> + drm_err(display->drm,
> + "Pipe %c FIFO underrun info: frame count: %u, line
> count: %u\n",
> + pipe_name(pipe),
> + REG_FIELD_GET(UNDERRUN_PIPE_FRAME_COUNT_MASK, val),
> + REG_FIELD_GET(UNDERRUN_LINE_COUNT_MASK, val));
> +}
> +
> +static void read_underrun_dbg_fbc(struct intel_display *display, enum pipe
> pipe, bool log)
> +{
> + enum intel_fbc_id fbc_id = intel_fbc_id_for_pipe(pipe);
> + u32 val = intel_de_read(display, FBC_DEBUG_STATUS(fbc_id));
> +
> + if (!(val & FBC_UNDERRUN_DECMPR))
> + return;
> +
> + intel_de_write(display, FBC_DEBUG_STATUS(fbc_id), FBC_UNDERRUN_DECMPR);
> +
> + if (log)
> + drm_err(display->drm,
> + "Pipe %c FIFO underrun info: FBC decompressing\n",
> + pipe_name(pipe));
> +}
> +
> +static void read_underrun_dbg_pkgc(struct intel_display *display, bool log)
> +{
> + u32 val = intel_de_read(display, GEN12_DCPR_STATUS_1);
> +
> + if (!(val & XE3P_UNDERRUN_PKGC))
> + return;
> +
> + /*
> + * Note: If there are multiple pipes enabled, only one of them will see
> + * XE3P_UNDERRUN_PKGC set.
> + */
> + intel_de_write(display, GEN12_DCPR_STATUS_1, XE3P_UNDERRUN_PKGC);
> +
> + if (log)
> + drm_err(display->drm,
> + "General FIFO underrun info: Package C-state blocking
> memory\n");
> +}
> +
> +static void read_underrun_dbg_info(struct intel_display *display,
> + enum pipe pipe,
> + bool log)
> +{
> + if (!HAS_UNDERRUN_DBG_INFO(display))
> + return;
> +
> + read_underrun_dbg1(display, pipe, log);
> + read_underrun_dbg2(display, pipe, log);
> + read_underrun_dbg_fbc(display, pipe, log);
> + read_underrun_dbg_pkgc(display, log);
> +}
> +
> static bool ivb_can_enable_err_int(struct intel_display *display)
> {
> struct intel_crtc *crtc;
> @@ -262,6 +377,17 @@ static bool
> __intel_set_cpu_fifo_underrun_reporting(struct intel_display *displa
> old = !crtc->cpu_fifo_underrun_disabled;
> crtc->cpu_fifo_underrun_disabled = !enable;
>
> + /*
> + * The debug bits get latched at the time of the FIFO underrun ISR bit
> + * getting set. That means that any existing debug bit that is set when
> + * handling a FIFO underrun interrupt has the potential to belong to
> + * another underrun event (past or future). To alleviate this problem,
> + * let's clear existing bits before enabling the interrupt, so that at
> + * least we don't get information that is too out-of-date.
> + */
> + if (enable && !old)
> + read_underrun_dbg_info(display, pipe, false);
> +
> if (HAS_GMCH(display))
> i9xx_set_fifo_underrun_reporting(display, pipe, enable, old);
> else if (display->platform.ironlake || display->platform.sandybridge)
> @@ -379,6 +505,8 @@ void intel_cpu_fifo_underrun_irq_handler(struct
> intel_display *display,
> trace_intel_cpu_fifo_underrun(display, pipe);
>
> drm_err(display->drm, "CPU pipe %c FIFO underrun\n",
> pipe_name(pipe));
> +
> + read_underrun_dbg_info(display, pipe, true);
> }
>
> intel_fbc_handle_fifo_underrun_irq(display);
--
Jani Nikula, Intel
