[lkml]   [2006]   [Mar]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: question on spi_bitbang

On Mar 31, 2006, at 1:07 PM, Kumar Gala wrote:

> On Mar 31, 2006, at 12:11 PM, David Brownell wrote:
>> On Friday 31 March 2006 9:31 am, Kumar Gala wrote:
>>> I'm looking at using spi_bitbang for a SPI driver and was trying to
>>> understand were the right point is to handle MODE switches.
>>> There are 4 function pointers provided for each mode.
>> That's if you are indeed "bit banging", or your controller is the
>> type that's basically a wrapper around a shift register: each
>> txrx_word() function transfers (or bitbangs) a 1-32 bit word in
>> the relevant SPI mode (0-3).
>> There's also a higher level txrx_bufs() routine for buffer-at-a-time
>> access, better suited to DMA, FIFOs, and half-duplex hardware.
> My controller is just a shift register that I can set the
> characteristics of (bit length for example, reverse data).
>>> My controller
>>> HW has a mode register which allows setting clock polarity and clock
>>> phase. I assume what I want is in my chipselect() function is to
>>> set
>>> my mode register and have the four function pointers set to the same
>>> function.
>> I don't know how your particular hardware works, but if you have a
>> real SPI controller it would probably be more natural to have your
>> setup() function handle that mode register earlier, out of the main
>> transfer loop ... unless that mode register is shared among all
>> chipselects, in which case you'd use the setup_transfer() call for
>> that, inside the transfer loop. (That call hasn't yet been merged
>> into the mainline kernel yet; it's in the MM tree.)
> The mode register is shared between chipselects so I'll go pull the
> patches from -mm for setup_transfer(). That sounds like the right
> place for setting my mode register.

Now that I look at setup_transfer() more I dont think its what I
want. It's only going to get called if the transfer is different
from the spi_device() settings. I would seem I would want to
configure all of my settings in chipselect().

>> The chipselect() call should only affect the chipselect signal and,
>> when you're activating a chip, its initial clock polarity. Though
>> if you're not using the latest from the MM tree, that's also your
>> hook for ensuring that the SPI mode is set up right.
> Why deal with just clock polarity and not clock phase as well in
> chipselect()?
> It sounds like with the new patch, I'll end up setting txrx_word[]
> to the same function for all modes.
> - kumar
> -
> To unsubscribe from this list: send the line "unsubscribe linux-
> kernel" in
> the body of a message to
> More majordomo info at
> Please read the FAQ at

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2006-03-31 21:19    [W:0.049 / U:2.148 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site