[PATCH] staging: fbtft: fix unaligned vmem writes when txbuf is byte-offset

[PATCH] staging: fbtft: fix unaligned vmem writes when txbuf is byte-offset

[suryasaimadhu]

fbtft_write_vmem16_bus8() and fb_ra8875's write_vmem16_bus8() offset
txbuf16 by one byte for a command/start prefix, then store 16-bit pixel
data via txbuf16[i]. On strict-alignment architectures this can fault
the same way as the write_reg path fixed in the previous patch.

Use put_unaligned() for these stores.

Signed-off-by: suryasaimadhu <suryasaimadhu369@gmail.com>
---
 drivers/staging/fbtft/fb_ra8875.c | 3 ++-
 drivers/staging/fbtft/fbtft-bus.c | 2 +-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/fbtft/fb_ra8875.c b/drivers/staging/fbtft/fb_ra8875.c
index 0ab1de664..5b95b0095 100644
--- a/drivers/staging/fbtft/fb_ra8875.c
+++ b/drivers/staging/fbtft/fb_ra8875.c
@@ -10,6 +10,7 @@
 #include <linux/delay.h>
 
 #include <linux/gpio/consumer.h>
+#include <linux/unaligned.h>
 #include "fbtft.h"
 
 #define DRVNAME "fb_ra8875"
@@ -262,7 +263,7 @@ static int write_vmem16_bus8(struct fbtft_par *par, size_t offset, size_t len)
 			to_copy, remain - to_copy);
 
 		for (i = 0; i < to_copy; i++)
-			txbuf16[i] = cpu_to_be16(vmem16[i]);
+			put_unaligned(cpu_to_be16(vmem16[i]), &txbuf16[i]);
 
 		vmem16 = vmem16 + to_copy;
 		ret = par->fbtftops.write(par, par->txbuf.buf,
diff --git a/drivers/staging/fbtft/fbtft-bus.c b/drivers/staging/fbtft/fbtft-bus.c
index cfcf4d7e7..fc3faab7d 100644
--- a/drivers/staging/fbtft/fbtft-bus.c
+++ b/drivers/staging/fbtft/fbtft-bus.c
@@ -158,7 +158,7 @@ int fbtft_write_vmem16_bus8(struct fbtft_par *par, size_t offset, size_t len)
 			to_copy, remain - to_copy);
 
 		for (i = 0; i < to_copy; i++)
-			txbuf16[i] = cpu_to_be16(vmem16[i]);
+			put_unaligned(cpu_to_be16(vmem16[i]), &txbuf16[i]);
 
 		vmem16 = vmem16 + to_copy;
 		ret = par->fbtftops.write(par, par->txbuf.buf,
-- 
2.47.3

Re: [PATCH] staging: fbtft: fix unaligned vmem writes when txbuf is byte-offset

[kernel test robot]

Hi suryasaimadhu,

kernel test robot noticed the following build errors:

[auto build test ERROR on staging/staging-testing]

url:    https://github.com/intel-lab-lkp/linux/commits/suryasaimadhu/staging-fbtft-fix-unaligned-vmem-writes-when-txbuf-is-byte-offset/20260625-190423
base:   staging/staging-testing
patch link:    https://lore.kernel.org/r/20260625110237.304435-1-suryasaimadhu369%40gmail.com
patch subject: [PATCH] staging: fbtft: fix unaligned vmem writes when txbuf is byte-offset
config: sh-allmodconfig (https://download.01.org/0day-ci/archive/20260625/202606252119.rClVa8On-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 16.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260625/202606252119.rClVa8On-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202606252119.rClVa8On-lkp@intel.com/

All errors (new ones prefixed by >>):

   drivers/staging/fbtft/fbtft-bus.c: In function 'fbtft_write_vmem16_bus8':
>> drivers/staging/fbtft/fbtft-bus.c:157:25: error: implicit declaration of function 'put_unaligned' [-Wimplicit-function-declaration]
     157 |                         put_unaligned(cpu_to_be16(vmem16[i]), &txbuf16[i]);
         |                         ^~~~~~~~~~~~~


vim +/put_unaligned +157 drivers/staging/fbtft/fbtft-bus.c

   113	
   114	/*****************************************************************************
   115	 *
   116	 *   int (*write_vmem)(struct fbtft_par *par);
   117	 *
   118	 *****************************************************************************/
   119	
   120	/* 16 bit pixel over 8-bit databus */
   121	int fbtft_write_vmem16_bus8(struct fbtft_par *par, size_t offset, size_t len)
   122	{
   123		u16 *vmem16;
   124		__be16 *txbuf16 = par->txbuf.buf;
   125		size_t remain;
   126		size_t to_copy;
   127		size_t tx_array_size;
   128		int i;
   129		int ret = 0;
   130		size_t startbyte_size = 0;
   131	
   132		remain = len / 2;
   133		vmem16 = (u16 *)(par->info->screen_buffer + offset);
   134	
   135		gpiod_set_value(par->gpio.dc, 1);
   136	
   137		/* non buffered write */
   138		if (!par->txbuf.buf)
   139			return par->fbtftops.write(par, vmem16, len);
   140	
   141		/* buffered write */
   142		tx_array_size = par->txbuf.len / 2;
   143	
   144		if (par->startbyte) {
   145			txbuf16 = par->txbuf.buf + 1;
   146			tx_array_size -= 2;
   147			*(u8 *)(par->txbuf.buf) = par->startbyte | 0x2;
   148			startbyte_size = 1;
   149		}
   150	
   151		while (remain) {
   152			to_copy = min(tx_array_size, remain);
   153			dev_dbg(par->info->device, "to_copy=%zu, remain=%zu\n",
   154				to_copy, remain - to_copy);
   155	
   156			for (i = 0; i < to_copy; i++)
 > 157				put_unaligned(cpu_to_be16(vmem16[i]), &txbuf16[i]);
   158	
   159			vmem16 = vmem16 + to_copy;
   160			ret = par->fbtftops.write(par, par->txbuf.buf,
   161							startbyte_size + to_copy * 2);
   162			if (ret < 0)
   163				return ret;
   164			remain -= to_copy;
   165		}
   166	
   167		return ret;
   168	}
   169	EXPORT_SYMBOL(fbtft_write_vmem16_bus8);
   170	

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] staging: fbtft: fix unaligned vmem writes when txbuf is byte-offset

[kernel test robot]

Hi suryasaimadhu,

kernel test robot noticed the following build errors:

[auto build test ERROR on staging/staging-testing]

url:    https://github.com/intel-lab-lkp/linux/commits/suryasaimadhu/staging-fbtft-fix-unaligned-vmem-writes-when-txbuf-is-byte-offset/20260625-190423
base:   staging/staging-testing
patch link:    https://lore.kernel.org/r/20260625110237.304435-1-suryasaimadhu369%40gmail.com
patch subject: [PATCH] staging: fbtft: fix unaligned vmem writes when txbuf is byte-offset
config: hexagon-allmodconfig (https://download.01.org/0day-ci/archive/20260625/202606252144.F56jkpaD-lkp@intel.com/config)
compiler: clang version 23.0.0git (https://github.com/llvm/llvm-project 6cc609bb250b21b47fc7d394b4019101e9983597)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260625/202606252144.F56jkpaD-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202606252144.F56jkpaD-lkp@intel.com/

All errors (new ones prefixed by >>):

>> drivers/staging/fbtft/fbtft-bus.c:157:4: error: call to undeclared function 'put_unaligned'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     157 |                         put_unaligned(cpu_to_be16(vmem16[i]), &txbuf16[i]);
         |                         ^
   1 error generated.


vim +/put_unaligned +157 drivers/staging/fbtft/fbtft-bus.c

   113	
   114	/*****************************************************************************
   115	 *
   116	 *   int (*write_vmem)(struct fbtft_par *par);
   117	 *
   118	 *****************************************************************************/
   119	
   120	/* 16 bit pixel over 8-bit databus */
   121	int fbtft_write_vmem16_bus8(struct fbtft_par *par, size_t offset, size_t len)
   122	{
   123		u16 *vmem16;
   124		__be16 *txbuf16 = par->txbuf.buf;
   125		size_t remain;
   126		size_t to_copy;
   127		size_t tx_array_size;
   128		int i;
   129		int ret = 0;
   130		size_t startbyte_size = 0;
   131	
   132		remain = len / 2;
   133		vmem16 = (u16 *)(par->info->screen_buffer + offset);
   134	
   135		gpiod_set_value(par->gpio.dc, 1);
   136	
   137		/* non buffered write */
   138		if (!par->txbuf.buf)
   139			return par->fbtftops.write(par, vmem16, len);
   140	
   141		/* buffered write */
   142		tx_array_size = par->txbuf.len / 2;
   143	
   144		if (par->startbyte) {
   145			txbuf16 = par->txbuf.buf + 1;
   146			tx_array_size -= 2;
   147			*(u8 *)(par->txbuf.buf) = par->startbyte | 0x2;
   148			startbyte_size = 1;
   149		}
   150	
   151		while (remain) {
   152			to_copy = min(tx_array_size, remain);
   153			dev_dbg(par->info->device, "to_copy=%zu, remain=%zu\n",
   154				to_copy, remain - to_copy);
   155	
   156			for (i = 0; i < to_copy; i++)
 > 157				put_unaligned(cpu_to_be16(vmem16[i]), &txbuf16[i]);
   158	
   159			vmem16 = vmem16 + to_copy;
   160			ret = par->fbtftops.write(par, par->txbuf.buf,
   161							startbyte_size + to_copy * 2);
   162			if (ret < 0)
   163				return ret;
   164			remain -= to_copy;
   165		}
   166	
   167		return ret;
   168	}
   169	EXPORT_SYMBOL(fbtft_write_vmem16_bus8);
   170	

--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] staging: fbtft: fix unaligned vmem writes when txbuf is byte-offset

[Andy Shevchenko]

On Thu, Jun 25, 2026 at 07:02:37PM +0800, suryasaimadhu wrote:
> fbtft_write_vmem16_bus8() and fb_ra8875's write_vmem16_bus8() offset
> txbuf16 by one byte for a command/start prefix, then store 16-bit pixel
> data via txbuf16[i]. On strict-alignment architectures this can fault
> the same way as the write_reg path fixed in the previous patch.

.write_reg()

Can you provide a real world example of the failure?

> Use put_unaligned() for these stores.

Sounds like a fix without Fixes tag.

> Signed-off-by: suryasaimadhu <suryasaimadhu369@gmail.com>

Use your name in accordance with your official documents.

...

> +++ b/drivers/staging/fbtft/fb_ra8875.c
> @@ -10,6 +10,7 @@
>  #include <linux/delay.h>

>  

You should move this blank line to be...

>  #include <linux/gpio/consumer.h>
> +#include <linux/unaligned.h>

...here.

>  #include "fbtft.h"

...

>  #define DRVNAME "fb_ra8875"

Are other drivers also being affected?

...

> +++ b/drivers/staging/fbtft/fbtft-bus.c

Also needs linux/unaligned.h.

> +			put_unaligned(cpu_to_be16(vmem16[i]), &txbuf16[i]);

-- 
With Best Regards,
Andy Shevchenko