linux-kernel - [PATCH v2] dmaengine: xilinx: xdma: Fix regmap max

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Message-Id: <20250901-xdma-max-reg-v2-1-fa3723a718cd@amarulasolutions.com>
Date: Mon, 01 Sep 2025 23:30:32 +0200
From: Anthony Brandon via B4 Relay <devnull+anthony.amarulasolutions.com@...nel.org>
To: Lizhi Hou <lizhi.hou@....com>, Brian Xu <brian.xu@....com>, 
 Raj Kumar Rampelli <raj.kumar.rampelli@....com>, 
 Vinod Koul <vkoul@...nel.org>, Michal Simek <michal.simek@....com>
Cc: dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, 
 Anthony Brandon <anthony@...rulasolutions.com>
Subject: [PATCH v2] dmaengine: xilinx: xdma: Fix regmap max_register

From: Anthony Brandon <anthony@...rulasolutions.com>

The max_register field is assigned the size of the register memory
region instead of the offset of the last register.
The result is that reading from the regmap via debugfs can cause
a segmentation fault:

tail /sys/kernel/debug/regmap/xdma.1.auto/registers
Unable to handle kernel paging request at virtual address ffff800082f70000
Mem abort info:
  ESR = 0x0000000096000007
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x07: level 3 translation fault
[...]
Call trace:
 regmap_mmio_read32le+0x10/0x30
 _regmap_bus_reg_read+0x74/0xc0
 _regmap_read+0x68/0x198
 regmap_read+0x54/0x88
 regmap_read_debugfs+0x140/0x380
 regmap_map_read_file+0x30/0x48
 full_proxy_read+0x68/0xc8
 vfs_read+0xcc/0x310
 ksys_read+0x7c/0x120
 __arm64_sys_read+0x24/0x40
 invoke_syscall.constprop.0+0x64/0x108
 do_el0_svc+0xb0/0xd8
 el0_svc+0x38/0x130
 el0t_64_sync_handler+0x120/0x138
 el0t_64_sync+0x194/0x198
Code: aa1e03e9 d503201f f9400000 8b214000 (b9400000)
---[ end trace 0000000000000000 ]---
note: tail[1217] exited with irqs disabled
note: tail[1217] exited with preempt_count 1
Segmentation fault

Signed-off-by: Anthony Brandon <anthony@...rulasolutions.com>
---
Changes in v2:
- Define new constant XDMA_MAX_REG_OFFSET and use that.
- Link to v1: https://lore.kernel.org/r/20250901-xdma-max-reg-v1-1-b6a04561edb1@amarulasolutions.com
---
 drivers/dma/xilinx/xdma-regs.h | 1 +
 drivers/dma/xilinx/xdma.c      | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/xilinx/xdma-regs.h b/drivers/dma/xilinx/xdma-regs.h
index 6ad08878e93862b770febb71b8bc85e66813428e..70bca92621aa41b0367d1e236b3e276344a26320 100644
--- a/drivers/dma/xilinx/xdma-regs.h
+++ b/drivers/dma/xilinx/xdma-regs.h
@@ -9,6 +9,7 @@
 
 /* The length of register space exposed to host */
 #define XDMA_REG_SPACE_LEN	65536
+#define XDMA_MAX_REG_OFFSET	(XDMA_REG_SPACE_LEN - 4)
 
 /*
  * maximum number of DMA channels for each direction:
diff --git a/drivers/dma/xilinx/xdma.c b/drivers/dma/xilinx/xdma.c
index 0d88b1a670e142dac90d09c515809faa2476a816..5ecf8223c112e468c79ce635398ba393a535b9e0 100644
--- a/drivers/dma/xilinx/xdma.c
+++ b/drivers/dma/xilinx/xdma.c
@@ -38,7 +38,7 @@ static const struct regmap_config xdma_regmap_config = {
 	.reg_bits = 32,
 	.val_bits = 32,
 	.reg_stride = 4,
-	.max_register = XDMA_REG_SPACE_LEN,
+	.max_register = XDMA_MAX_REG_OFFSET,
 };
 
 /**

---
base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
change-id: 20250901-xdma-max-reg-1649c6459358

Best regards,
-- 
Anthony Brandon <anthony@...rulasolutions.com>