On 20 March 2016 18:15:50 GMT+00:00, Joachim Eastwood <manabian@xxxxxxxxx> wrote:
>Hi Jonathan,
>
>On 20 March 2016 at 18:25, Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
>> On 20/03/16 16:12, Joachim Eastwood wrote:
>>>> +static int mcp4131_exec(struct mcp4131_data *data,
>>>> + u8 addr, u8 cmd,
>>>> + u16 val)
>>>> +{
>>>> + int err;
>>>> + struct spi_device *spi = data->spi;
>>>> +
>>>> + data->xfer.tx_buf = data->buf;
>>>> + data->xfer.rx_buf = data->buf;
>>>> +
>>>> + switch (cmd) {
>>>> + case MCP4131_READ:
>>>> + data->xfer.len = 2; /* Two bytes transfer for this
>command */
>>>> + data->buf[0] = (addr << MCP4131_WIPER_SHIFT) |
>MCP4131_READ;
>>>> + data->buf[1] = 0;
>>>> + break;
>>>> +
>>>> + case MCP4131_WRITE:
>>>> + data->xfer.len = 2;
>>>> + data->buf[0] = (addr << MCP4131_WIPER_SHIFT) |
>>>> + MCP4131_WRITE | (val >> 8);
>>>> + data->buf[1] = val & 0xFF; /* 8 bits here */
>>>> + break;
>>>> +
>>>> + default:
>>>> + return -EINVAL;
>>>> + }
>>>> +
>>>> + dev_dbg(&spi->dev, "mcp4131_exec: tx0: 0x%x tx1: 0x%x\n",
>>>> + data->buf[0], data->buf[1]);
>>>> +
>>>> + spi_message_init(&data->msg);
>>>> + spi_message_add_tail(&data->xfer, &data->msg);
>>>> +
>>>> + err = spi_sync(spi, &data->msg);
>>>> + if (err) {
>>>> + dev_err(&spi->dev, "spi_sync(): %d\n", err);
>>>> + return err;
>>>> + }
>>>
>>> Isn't this init, add, sync sequence basically open coding of what
>>> spi_write/spi_read does?
>>> If you could use those you could also get rid transfer/message
>structs
>>> in priv data.
>> I initially wrote the same comment, then realised it's more nuanced
>than
>> that. Whilst this initially looks like an w8r8 type cycle it's
>actually
>> something like w4r12 in the read case anyway. The write case could
>indeed
>> be done with spi_write.
>
>Indeed. I didn't notice that for the read case.
>
>The read case could almost be copy of spi_read, though. One would only
>need to add ".tx_buf = buf" when setting up the transfer struct, I
>think. Having it in its a own function with a comment would make it
>easier to spot the difference.
Agreed
>
>
>regards,
>Joachim Eastwood
--
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