Can't write to IIC by I2CRDWR with two records 'struct iic_msg'

[Ian Lepore]

On Sun, 2019-11-10 at 16:55 +0400, mishin at mh.san.ru wrote:
> About a system:
> 1. FreeBSD betta 12.1-STABLE FreeBSD 12.1-STABLE r354236
> OPI_ZERO  arm
> 2. Allwinner H2+
> 3.
> iichb0: <Allwinner Integrated I2C Bus Controller> mem 
> 0x1c2ac00-0x1c2afff irq 35 on simplebus0
> iicbus0: <OFW I2C bus> on iichb0
> iic0: <I2C generic I/O> on iicbus0
> 
> 
> I trying to send a data array following a register value to a
> SSD1306 
> display
> from 'Allwinner H2+' by a following method (according to `i2c.c`):
> 
> char SSD1306::iic_write(uint8_t offset, uint8_t data[], uint16_t
> size) 
> const {
>    struct iic_msg msgs[2] =
>    {
>      {slave_addr, IIC_M_WR | IIC_M_NOSTOP, sizeof(offset), &offset},
>      {slave_addr, IIC_M_WR | IIC_M_NOSTART, size, data}
>    };

Some i2c hardware controller drivers don't properly support the NOSTOP
and NOSTART flags.  Sometimes it's a bug, and sometimes it's because
hardware limitations prevent it.  In the allwinner case, I think it's a
bug, but manu would know for sure.

-- Ian


>    struct iic_rdwr_data xfer = {msgs, 2};
> 
>    if ( ioctl(iic_handle, I2CRDWR, &xfer) == -1 )  {
>      perror("ioctl(I2CRDWR)");
>      return(-1);
>    };
>    return(0);
> };
> 
> iic_write(0x40, buffer, buffer_size);
> 
> But something goes wrong and the display stills blank (no errors, 
> though). But when I use an 'one record' struct
> with combined 'register+data' array (see below) or read by that 'two 
> records' scheme (see below), all is ok.
> 
> Have I made a mistake is flags or it is a feature or a bug?
> 
> Thanks
> 
> 
> 
> 
> ---
> Next two methods works ok
> 
> Read following write:
> char TEA5767::iic_read(uint8_t offset, uint8_t *data, uint16_t size) 
> const {
>    struct iic_msg msgs[2] =
>    {
>      {slave_addr, IIC_M_WR | IIC_M_NOSTOP, sizeof(offset), &offset},
>      {slave_addr, IIC_M_RD, size, data}
>    };
>    struct iic_rdwr_data xfer = {msgs, 2};
> 
>    if ( ioctl(iic_handle, I2CRDWR, &xfer) == -1)  {
>      perror("ioctl(I2CRDWR)");
>      return(-1);
>    };
>    return(0);
> };
> 
> and write a combined 'register+data' array works too:
> 
> char SSD1306::iic_write(uint8_t data[], uint16_t size) const
> {
>    struct iic_msg msgs[1] =
>    {
>      {slave_addr, IIC_M_WR, size, data}
>    };
>    struct iic_rdwr_data xfer = {msgs, 1};
> 
>    if ( ioctl(iic_handle, I2CRDWR, &xfer) == -1)  {
>      perror("ioctl(I2CRDWR)");
>      return(-1);
>    };
>    return(0);
> }
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