The snapshotting code internally aligns data segment to 16 bytes. This
works fine for DPU code (where most of the regions are aligned), but
fails for snapshotting of the DSI data (because DSI data region is
shifted by 4 bytes). Fix the code by removing length alignment and by
accurately printing last registers in the region. While reworking the
code also fix the 16x memory overallocation in
msm_disp_state_dump_regs().

Fixes: 98659487b845 ("drm/msm: add support to take dpu snapshot")
Reported-by: Salendarsingh Gaud <sgaud@qti.qualcomm.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
 drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c | 27 ++++++++++++++++++-----
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c b/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
index 5e151952dea8..a86c7fc46f68 100644
--- a/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
+++ b/drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c
@@ -9,7 +9,7 @@
 
 #include "msm_disp_snapshot.h"
 
-static void msm_disp_state_dump_regs(u32 **reg, u32 aligned_len, void __iomem *base_addr)
+static void msm_disp_state_dump_regs(u32 **reg, u32 len, void __iomem *base_addr)
 {
 	u32 len_padded;
 	u32 num_rows;
@@ -19,11 +19,11 @@ static void msm_disp_state_dump_regs(u32 **reg, u32 aligned_len, void __iomem *b
 	void __iomem *end_addr;
 	int i;
 
-	len_padded = aligned_len * REG_DUMP_ALIGN;
-	num_rows = aligned_len / REG_DUMP_ALIGN;
+	len_padded = round_up(len, REG_DUMP_ALIGN);
+	num_rows = DIV_ROUND_UP(len, REG_DUMP_ALIGN);
 
 	addr = base_addr;
-	end_addr = base_addr + aligned_len;
+	end_addr = base_addr + len;
 
 	*reg = kvzalloc(len_padded, GFP_KERNEL);
 	if (!*reg)
@@ -48,8 +48,8 @@ static void msm_disp_state_dump_regs(u32 **reg, u32 aligned_len, void __iomem *b
 static void msm_disp_state_print_regs(const u32 *dump_addr, u32 len,
 		void __iomem *base_addr, struct drm_printer *p)
 {
+	void __iomem *addr, *end_addr;
 	int i;
-	void __iomem *addr;
 	u32 num_rows;
 
 	if (!dump_addr) {
@@ -58,6 +58,7 @@ static void msm_disp_state_print_regs(const u32 *dump_addr, u32 len,
 	}
 
 	addr = base_addr;
+	end_addr = base_addr + len;
 	num_rows = len / REG_DUMP_ALIGN;
 
 	for (i = 0; i < num_rows; i++) {
@@ -67,6 +68,17 @@ static void msm_disp_state_print_regs(const u32 *dump_addr, u32 len,
 				dump_addr[i * 4 + 2], dump_addr[i * 4 + 3]);
 		addr += REG_DUMP_ALIGN;
 	}
+
+	if (addr != end_addr) {
+		drm_printf(p, "0x%lx : %08x",
+			   (unsigned long)(addr - base_addr),
+			   dump_addr[i * 4]);
+		if (addr + 0x4 < end_addr)
+			drm_printf(p, " %08x", dump_addr[i * 4 + 1]);
+		if (addr + 0x8 < end_addr)
+			drm_printf(p, " %08x", dump_addr[i * 4 + 2]);
+		drm_printf(p, "\n");
+	}
 }
 
 void msm_disp_state_print(struct msm_disp_state *state, struct drm_printer *p)
@@ -172,6 +184,9 @@ void msm_disp_snapshot_add_block(struct msm_disp_state *disp_state, u32 len,
 	struct va_format vaf;
 	va_list va;
 
+	if (strcmp(fmt, "dsi%d_ctrl"))
+		return;
+
 	new_blk = kzalloc_obj(struct msm_disp_state_block);
 	if (!new_blk)
 		return;
@@ -185,7 +200,7 @@ void msm_disp_snapshot_add_block(struct msm_disp_state *disp_state, u32 len,
 	va_end(va);
 
 	INIT_LIST_HEAD(&new_blk->node);
-	new_blk->size = ALIGN(len, REG_DUMP_ALIGN);
+	new_blk->size = len;
 	new_blk->base_addr = base_addr;
 
 	msm_disp_state_dump_regs(&new_blk->state, new_blk->size, base_addr);

---
base-commit: 11ff30385c8ad7de9862f4f1cec424fca15a4f13
change-id: 20260515-msm-fix-dsi-dump-2-64a3bc160da6

Best regards,
--  
With best wishes
Dmitry

On Sat, May 16, 2026 at 12:40:10AM +0300, Dmitry Baryshkov wrote:
> The snapshotting code internally aligns data segment to 16 bytes. This
> works fine for DPU code (where most of the regions are aligned), but
> fails for snapshotting of the DSI data (because DSI data region is
> shifted by 4 bytes). Fix the code by removing length alignment and by
> accurately printing last registers in the region. While reworking the
> code also fix the 16x memory overallocation in
> msm_disp_state_dump_regs().
> 
> Fixes: 98659487b845 ("drm/msm: add support to take dpu snapshot")
> Reported-by: Salendarsingh Gaud <sgaud@qti.qualcomm.com>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
> ---
>  drivers/gpu/drm/msm/disp/msm_disp_snapshot_util.c | 27 ++++++++++++++++++-----
>  1 file changed, 21 insertions(+), 6 deletions(-)
> 
> @@ -172,6 +184,9 @@ void msm_disp_snapshot_add_block(struct msm_disp_state *disp_state, u32 len,
>  	struct va_format vaf;
>  	va_list va;
>  
> +	if (strcmp(fmt, "dsi%d_ctrl"))
> +		return;
> +

And this is a debugging change, which I forgot to remove. I'll send v2.

>  	new_blk = kzalloc_obj(struct msm_disp_state_block);
>  	if (!new_blk)
>  		return;

-- 
With best wishes
Dmitry