On 2015-04-09 17:40, Mark Brown wrote:
> Why is the callback mandatory if an empty implementation is OK?
Ask the author of spi-bitbang. :-)
In spi_bitbang_start() we have this chunk of code:
if (!bitbang->txrx_bufs) {
bitbang->use_dma = 0;
bitbang->txrx_bufs = spi_bitbang_bufs;
if (!master->setup) {
if (!bitbang->setup_transfer)
bitbang->setup_transfer =
spi_bitbang_setup_transfer;
master->setup = spi_bitbang_setup;
master->cleanup = spi_bitbang_cleanup;
}
}
As can be seen here, if setup_transfer is NULL (not set by the
specific driver), it is filled in with the default callback function
spi_bitbang_setup_transfer(), but only if txrx_bufs is also NULL,
which is not the case here.
There is a comment in spi-xilinx also stating this fact (though their
implementation isn't actually empty anymore):
/* spi_bitbang requires custom setup_transfer() to be defined if there
is a
* custom txrx_bufs().
*/
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