* [PATCH] staging: sm750fb: Refactor init_status to use initchip_param
2026-07-19 19:58 [PATCH] staging: sm750fb: select FB_IOMEM_FOPS in Kconfig MishraMohit21
@ 2026-07-19 19:58 ` MishraMohit21
2026-07-20 7:50 ` [PATCH] staging: sm750fb: select FB_IOMEM_FOPS in Kconfig Ahmet Sezgin Duran
1 sibling, 0 replies; 3+ messages in thread
From: MishraMohit21 @ 2026-07-19 19:58 UTC (permalink / raw)
To: Sudip Mukherjee, Teddy Wang, Greg Kroah-Hartman
Cc: linux-fbdev, linux-staging, linux-kernel, MishraMohit21
The driver initializes the hardware by casting 'struct init_status *' to
'struct initchip_param *' in ddk750_init_hw(). This is technically
undefined behavior, violates strict-aliasing rules, and is fragile.
Furthermore, 'struct init_status' defines the 'reset_memory' field as a
2-byte 'ushort', while 'struct initchip_param' defines it as a 1-byte
'unsigned char'. On little-endian architectures, reading the low byte
of the ushort happens to evaluate to the correct value (0 or 1) by accident.
However, on big-endian architectures, casting and reading this field
reads the high byte (0x00) instead, causing a silent failure where the
memory controller is never reset.
This endianness layout mismatch was empirically verified using a standalone
test harness (scratch/be_test.c) compiled under a mips-linux-gnu-gcc
cross-compiler and executed under qemu-mips.
Resolve this by removing the duplicate 'struct init_status' entirely and
using 'struct initchip_param' directly. This removes the unsafe pointer
cast and ensures endian-safe hardware initialization.
This change has been compile-tested only. No hardware was available to
verify runtime behavior.
Signed-off-by: MishraMohit21 <mishraloopmohit@gmail.com>
---
drivers/staging/sm750fb/sm750.c | 8 ++++----
drivers/staging/sm750fb/sm750.h | 12 ++----------
drivers/staging/sm750fb/sm750_hw.c | 16 ++++++++--------
3 files changed, 14 insertions(+), 22 deletions(-)
diff --git a/drivers/staging/sm750fb/sm750.c b/drivers/staging/sm750fb/sm750.c
index 89c811e0806c..5986dbef67c0 100644
--- a/drivers/staging/sm750fb/sm750.c
+++ b/drivers/staging/sm750fb/sm750.c
@@ -844,11 +844,11 @@ static void sm750fb_setup(struct sm750_dev *sm750_dev, char *src)
swap = 0;
- sm750_dev->init_parm.chip_clk = 0;
- sm750_dev->init_parm.mem_clk = 0;
- sm750_dev->init_parm.master_clk = 0;
+ sm750_dev->init_parm.chip_clock = 0;
+ sm750_dev->init_parm.mem_clock = 0;
+ sm750_dev->init_parm.master_clock = 0;
sm750_dev->init_parm.power_mode = 0;
- sm750_dev->init_parm.setAllEngOff = 0;
+ sm750_dev->init_parm.set_all_eng_off = 0;
sm750_dev->init_parm.reset_memory = 1;
/* defaultly turn g_hwcursor on for both view */
diff --git a/drivers/staging/sm750fb/sm750.h b/drivers/staging/sm750fb/sm750.h
index d2c522e67f26..313c2683bf6c 100644
--- a/drivers/staging/sm750fb/sm750.h
+++ b/drivers/staging/sm750fb/sm750.h
@@ -38,15 +38,7 @@ enum sm750_path {
sm750_pnc = 3, /* panel and crt */
};
-struct init_status {
- ushort power_mode;
- /* below three clocks are in unit of MHZ*/
- ushort chip_clk;
- ushort mem_clk;
- ushort master_clk;
- ushort setAllEngOff;
- ushort reset_memory;
-};
+#include "ddk750_chip.h"
struct lynx_accel {
/* base virtual address of DPR registers */
@@ -102,7 +94,7 @@ struct sm750_dev {
/* locks*/
spinlock_t slock;
- struct init_status init_parm;
+ struct initchip_param init_parm;
enum sm750_pnltype pnltype;
enum sm750_dataflow dataflow;
int nocrt;
diff --git a/drivers/staging/sm750fb/sm750_hw.c b/drivers/staging/sm750fb/sm750_hw.c
index 34a837fb4b64..54c1b241ae6e 100644
--- a/drivers/staging/sm750fb/sm750_hw.c
+++ b/drivers/staging/sm750fb/sm750_hw.c
@@ -66,20 +66,20 @@ int hw_sm750_map(struct sm750_dev *sm750_dev, struct pci_dev *pdev)
int hw_sm750_inithw(struct sm750_dev *sm750_dev, struct pci_dev *pdev)
{
- struct init_status *parm;
+ struct initchip_param *parm;
parm = &sm750_dev->init_parm;
- if (parm->chip_clk == 0)
- parm->chip_clk = (sm750_get_chip_type() == SM750LE) ?
+ if (parm->chip_clock == 0)
+ parm->chip_clock = (sm750_get_chip_type() == SM750LE) ?
DEFAULT_SM750LE_CHIP_CLOCK :
DEFAULT_SM750_CHIP_CLOCK;
- if (parm->mem_clk == 0)
- parm->mem_clk = parm->chip_clk;
- if (parm->master_clk == 0)
- parm->master_clk = parm->chip_clk / 3;
+ if (parm->mem_clock == 0)
+ parm->mem_clock = parm->chip_clock;
+ if (parm->master_clock == 0)
+ parm->master_clock = parm->chip_clock / 3;
- ddk750_init_hw((struct initchip_param *)&sm750_dev->init_parm);
+ ddk750_init_hw(&sm750_dev->init_parm);
/* for sm718, open pci burst */
if (sm750_dev->devid == 0x718) {
poke32(SYSTEM_CTRL,
--
2.43.0
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] staging: sm750fb: select FB_IOMEM_FOPS in Kconfig
2026-07-19 19:58 [PATCH] staging: sm750fb: select FB_IOMEM_FOPS in Kconfig MishraMohit21
2026-07-19 19:58 ` [PATCH] staging: sm750fb: Refactor init_status to use initchip_param MishraMohit21
@ 2026-07-20 7:50 ` Ahmet Sezgin Duran
1 sibling, 0 replies; 3+ messages in thread
From: Ahmet Sezgin Duran @ 2026-07-20 7:50 UTC (permalink / raw)
To: MishraMohit21, Sudip Mukherjee, Teddy Wang, Greg Kroah-Hartman
Cc: linux-fbdev, linux-staging, linux-kernel
On 7/19/26 10:58 PM, MishraMohit21 wrote:
> The driver uses the FB_DEFAULT_IOMEM_OPS macro in sm750.c to define its
> framebuffer operations. This macro references core framebuffer operations
> fb_io_read, fb_io_write, and fb_io_mmap. These symbols are defined in
> fb_io_fops.c, which is compiled only under CONFIG_FB_IOMEM_FOPS.
>
> Since config FB_SM750 does not currently select FB_IOMEM_FOPS, compiling
> the driver on a config that has no other framebuffer drivers enabled
> fails with undefined symbol link errors during MODPOST.
>
> Add 'select FB_IOMEM_FOPS' to Kconfig to ensure the driver core helpers
> build successfully in all configurations. Keep the select statements
> sorted alphabetically.
>
> Signed-off-by: MishraMohit21 <mishraloopmohit@gmail.com>
> ---
> drivers/staging/sm750fb/Kconfig | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/staging/sm750fb/Kconfig b/drivers/staging/sm750fb/Kconfig
> index 08bcccdd0f1c..7d5ad423e41f 100644
> --- a/drivers/staging/sm750fb/Kconfig
> +++ b/drivers/staging/sm750fb/Kconfig
> @@ -2,10 +2,11 @@
> config FB_SM750
> tristate "Silicon Motion SM750 framebuffer support"
> depends on FB && PCI && HAS_IOPORT
> - select FB_MODE_HELPERS
> - select FB_CFB_FILLRECT
> select FB_CFB_COPYAREA
> + select FB_CFB_FILLRECT
> select FB_CFB_IMAGEBLIT
> + select FB_IOMEM_FOPS
> + select FB_MODE_HELPERS
> help
> Frame buffer driver for the Silicon Motion SM750 chip
> with 2D acceleration and dual head support.
Does not apply to Greg's staging-testing branch. `FB_IOMEM_FOPS` already
exists in Kconfig.
Also you need to put a fullname in `Signed-off-by` part.
Regards,
Ahmet Sezgin Duran
^ permalink raw reply [flat|nested] 3+ messages in thread