[q] what is max SPI transfer size ?

[Sfinx]

while trying to send 256 bytes I'm seeing the corruption/driver freeze after size of 121. Is this is limitation of the driver or ch341 chip itself ?

[frank-zago]

The max size is set to 124 in the driver (cha341_spi_max_tx_size). I've tested large transfer talking to some SPI displays, but maybe linux never reached that size???

[Sfinx]

Seems like there is no size error check somewhere as trying to send 128 bytes with SPI_IOC_MESSAGE will hang the driver - no further interactions possible, only rmmod/insmod ch341_buses.ko will bring it to live again.

Will something like this work for increasing transfer size ?

diff --git a/ch341-spi.c b/ch341-spi.c
index 432b9b5..19f8751 100644
--- a/ch341-spi.c
+++ b/ch341-spi.c
@@ -48,7 +48,7 @@ static const struct spi_gpio spi_gpio_cs[CH341_SPI_MAX_NUM_DEVICES] = {
 
 static size_t cha341_spi_max_tx_size(struct spi_device *spi)
 {
-       return CH341_SPI_NSEGS * (SEG_SIZE - 1);
+       return CH341_SPI_NSEGS * (CH341_SPI_SEG_SIZE - 1);
 }
 
 /* Send a command and get a reply if requested */
@@ -69,7 +69,7 @@ static int spi_transfer(struct ch341_device *dev, u8 *buf, int len, int nsegs)
        do {
                rc = usb_bulk_msg(dev->usb_dev,
                                  usb_rcvbulkpipe(dev->usb_dev, dev->ep_in),
-                                 &buf[sz_read], SEG_SIZE, &actual, DEFAULT_TIMEOUT);
+                                 &buf[sz_read], CH341_SPI_SEG_SIZE, &actual, DEFAULT_TIMEOUT);
 
                if (rc == 0)
                        sz_read += actual;
@@ -102,12 +102,12 @@ static unsigned int copy_to_device(u8 *buf, unsigned int buf_idx,
        int to_copy;
 
        while (len) {
-               if (buf_idx % SEG_SIZE == 0) {
+               if (buf_idx % CH341_SPI_SEG_SIZE == 0) {
                        buf[buf_idx] = CH341_CMD_SPI_STREAM;
                        buf_idx++;
                }
 
-               to_copy = min(len, SEG_SIZE - (buf_idx % SEG_SIZE));
+               to_copy = min(len, CH341_SPI_SEG_SIZE - (buf_idx % CH341_SPI_SEG_SIZE));
 
                if (tx_buf) {
                        if (lsb)
diff --git a/ch341.h b/ch341.h
index 56488df..5e24efe 100644
--- a/ch341.h
+++ b/ch341.h
@@ -25,6 +25,7 @@
  * crash if more than 4.
  */
 #define CH341_SPI_NSEGS 4
+#define CH341_SPI_SEG_SIZE 64
 
 #define CH341_USB_MAX_INTR_SIZE 8
 
@@ -74,7 +75,7 @@ struct ch341_device {
        struct spi_client {
                struct spi_device *slave;
                struct gpio_desc *gpio;
-               u8 buf[CH341_SPI_NSEGS * SEG_SIZE];
+               u8 buf[CH341_SPI_NSEGS * CH341_SPI_SEG_SIZE];
        } spi_clients[CH341_SPI_MAX_NUM_DEVICES];
 };

[frank-zago]

That's not correct. The chip is using 32-bytes segments, not 64.

I tested again with an eeprom using the spi-nor driver. I saw no issue, and the max transfer size was always 128 bytes.

What are you doing to see corruption?

[Sfinx]

I needed 256 bytes, 128 is not enough. The driver module just hangs if transfer size is bigger 128. I see, seems like 128b is somewhat unknown limit.