SPI configuration

14Og · June 21, 2024, 4:33pm

Hi there! I’ve been working with spi interface of duo using spidev linux library, and found out that maximum tx buffer size to send data is 4096 bytes. I can not change file /sys/module/spidev/parameters/bufsize as it is write-protected, so i wonder, is there a legal way to increase spi buffer size? It seems to me, that i can change this value when building duo-buildroot-sdk, but i also couldn’t find any configs related to that in repository. Thanks in advance!

mark.birss · June 21, 2024, 7:32pm

To support running metastatic i use loadable kernel modules

Specify the bufsize as option

insmod /lib/modules/5.10.4-tag-/drivers/spi/spidev.ko bufsiz=20480

Have SPI LoRa SX1262 and 3.5" 320x480 SPI Display here
Milk-V DUO 256

And

Milk-V DUO 64 with USB keyboard mouse input 2.0" 320x240 SPI Display and SPI SX1262 LoRa

14Og · June 24, 2024, 8:13am

yep, this is great idea, but i’d like to keep default buildroot-sdk image as i’m also working with camera sdk. Maybe someone knows how to change this bufsiz varaible from buildroot side? I can see sources of spidev driver in buildroot-sdk repo in duo-buildroot-sdk/linux_5.10/drivers/spi/spidev.c and there is bufsiz variable. Can i simply change it to my desired value and rebuild image w/o any unexpected consequences? Thank you!

mark.birss · June 24, 2024, 8:24am

Ok, i did also try to pass the parameter from u-boot but my attempts it did stop the boot process for some reason

github.com

milkv-duo/duo-buildroot-sdk/blob/66daf080a375e2f7082a51fe02596a71b67fcbc8/u-boot-2021.10/include/configs/cv181x-asic.h#L289


      
          		#elif defined(CONFIG_SPI_FLASH)
          			#define LOAD_LOGO "sf probe;sf read " LOGO_READ_ADDR " ${MISC_PART_OFFSET} ${MISC_PART_SIZE};"
          		#else
          			#define LOAD_LOGO "mmc dev 0;mmc read " LOGO_READ_ADDR " ${MISC_PART_OFFSET} ${MISC_PART_SIZE};"
          		#endif
          		#define SHOWLOGOCOMMAND LOAD_LOGO CVI_JPEG START_VO START_VL SET_VO_BG
          	#else
          		#define SHOWLOGOCMD
          	#endif
          
          	#define SET_BOOTARGS "setenv bootargs ${reserved_mem} ${root} ${mtdparts} " \
          					"console=$consoledev,$baudrate $othbootargs;"
          
          	#define SD_BOOTM_COMMAND \
          				SET_BOOTARGS \
          				"echo Boot from SD ...;" \
          				"mmc dev 0 && fatload mmc 0 ${uImage_addr} boot.sd; " \
          				"if test $? -eq 0; then " \
          				UBOOT_VBOOT_BOOTM_COMMAND \
          				"fi;"

but you could edit the kernel source and change the default size ?
./linux_5.10/drivers/spi/
spidev.c

line 85
static unsigned bufsiz = 4096;

14Og · June 24, 2024, 8:36am

Yep, i did it right now, image built successfully within docker, i’ll test the results and let you know about it.

14Og · June 24, 2024, 9:02am

Well, as i expected, it couldn’t be so easy) Right now i have bufsiz 32768 bytes in /sys/module/spidev/parameters that i changed in spidev sources of buildroot drivers. Spidev still working fine, i can transfer data, but maximum tx buffer size is still 4096, and when im trying to transfer message more than 4096 bytes i got return code -1 from ioctl.

It seems to me, that i need to change something else to let kernel know that bufsiz is more than 4096…

mark.birss · June 24, 2024, 9:23am

Oh, i set to max 32767

cat /sys/module/spidev/parameters/bufsiz ?

14Og · June 24, 2024, 9:26am

it is 32768, which is funny

mark.birss · June 24, 2024, 9:26am

oh ok i see, not sure where else then

I finish my pcb breakout now (DUO 64 and DUO 256)

bhupiister · November 27, 2025, 1:04am

I am having an issue where i am unable to connect ILI9486 to milk-v duo s module sg2000

SPI bus used is spi3. Tried modifying the defconfig and dts file as per various post on this community channel, but still no output. While dmesg it shows SPI0 whereas i am connecting it to SPI3

LCD used https://www.waveshare.com/wiki/3.5inch_RPi_LCD_(B)

Evaluation Module used