On Wed, May 21, 2008 at 11:05 AM, Anton Vorontsov <[EMAIL PROTECTED]> wrote: > On Wed, May 21, 2008 at 10:50:02AM -0600, Grant Likely wrote: > [..] >> > + >> > + master->num_chipselect = of_num_children(np); >> >> This assumes that there are no gaps in the assigned CS numbers of >> child nodes, or that the child nodes are an exhaustive list of >> attached devices, neither of which may be true. num_chipselect should >> be calculated from the number of GPIOs specified instead. > > [I'm not arguing just a thought.]
:-) Here's some quick feedback off the top of my head... > - every SPI device must have its own chip-select, otherwise SPI device > node should not be a part of a SPI controller node; How about this example: Board has SPI controller with 4 CS lines and 4 devices. Board vendor has 3 versions of board with different devices populated (Ver1 has all 4; Ver2 has 1 and 3; Ver3 has 1, 3 and 4). Board firmware drops nodes from tree for non-present devices before booting kernel (not arguing if this is the best way for firmware to behave; but it is valid and legal). Therefore there may be gaps in the CS assignments. Or how about this one: the SPI devices are off board and are plugged in after boot. They aren't available to be described in the device tree, but are added at a later time in response to some hot plug event. The SPI bus needs to be already set up with the correct number of CS lines. I don't think you can assume that the device tree data will be exhaustive. > - or there is just once device on the SPI bus with chip-select always > asserted, no gpios = <> is specified (this case is implemented); > - or the SPI is bridged, gpios = <> should list behind-the-bridge devices' > chip-selects, and driver should understand that there is a "special" > (bridge) device somewhere on the bus (not implemented). In this case, I think the gpios would be a property of the spi-bridge, not the spi-master. The gpios of the spi-master would have to specify how to address the bridge; not the downstream devices. The bridge; when addressed correctly; would then proceed with addressing the downstream. In other words; the 'reg' of spi-devices attached to a bridge would be an address that the bridge understands, not an address that the master understands. Cheers, g. -- Grant Likely, B.Sc., P.Eng. Secret Lab Technologies Ltd. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
