Nicolas Ferre a écrit :
As the SPI underlying code behaves quite differently from a
controller driver
to another whan not having a tx_buf filled, I have add a zerroed
buffer to give
to the spi layer while receiving data.
You must be working with a buggy controller driver then. That part of
this patch should never be needed. It's expected that rx-only transfers
will omit a tx buf; all controller drivers must handle that case.
I said that because it is true that most of spi controller drivers
manage rx only transactions filling the tx buffer with zerros but the
spi_s3c24xx.c driver seems to fill with ones (line 177 hw_txbyte())
Anyway, I will check in our controller driver to sort this out.
I dug a bit into this.
Well, in the atmel_spi driver code, we use previous rx buffer if we do
not provide a tx_buf (as it is said that in struct spi_transfer
comments, "If the transmit buffer is null, undefined data will be
shifted out while filling rx_buf").
So, the touchscreen controller sees sometimes a "start" condition (bit 7
of a control byte). It then takes the control byte and sets trash bits
as a configuration. I ran into those troubles and add a zerroed buffer
as tx.
Do you think that shifting zerros out when a tx_buf is not specified is
the desired behavior ?
Regards,
--
Nicolas Ferre
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