[Question] m25p80 driver versus spi clock rate
david-b at pacbell.net
Tue Jun 23 15:56:19 EDT 2009
On Tuesday 23 June 2009, Mike Frysinger wrote:
> On Tue, Jun 23, 2009 at 14:41, Steven A. Falco wrote:
> > Mike Frysinger wrote:
> >> On Mon, Jun 22, 2009 at 16:50, Steven A. Falco wrote:
> >>> I am trying to figure out how the mtd/devices/m25p80.c driver is supposed
> >>> to set the spi clock speed. (Perhaps I'm making a bad assuption even to
> >>> think that it _should_ set the clock speed. If so, please say so.)
> >> it shouldnt. this is done in the board resources via the speed_hz
> >> field of the spi_board_info struct on a per-spi device setting.
> > Thank you for the hint. spi_board_info has a max_speed_hz field - it does
> > not have a speed_hz field. The various platforms all seem to set
> > max_speed_hz, so perhaps that is what you meant to say.
Right. A chip might support a much faster rate than is
achievable on a given board. That's why setting the speed
limit is one of the duties of the board-specific setup code.
> > In my case, max_speed_hz is being correctly set, but that doesn't seem to be
> > enough. I have traced through the calling hierarchy, and this is what I got:
> > 1) m25p80_read builds a spi_message, and calls spi_sync to do the transfer.
> > 2) spi_sync calls spi_async. I added some printk, and saw speed_hz=0 and
> > max_speed_hz=50000000. This is consistent with my platform setup (set via
> > a dts file).
What code are you talking about then? Not the m25p80 code,
which just depends on platform code to have done its job.
> > 3) spi_async calls through pointer "transfer" to spi_bitbang_transfer (because
> > the PPC4xx driver doesn't set its own transfer handler).
> > 4) spi_bitbang_transfer calls spi_master_get_devdata, then enqueues the work
> > 5) bitbang_work iterates through the queued transfers, and if speed_hz is
> > non-zero, bitbang_work calls through setup_transfer to spi_ppc4xx_setupxfer
> > which would set the divisor. But, as noted in step 2, speed_hz=0, so the
> > spi bus speed is not set. Rather, it remains at whatever speed some other
> > device chose.
> > Note that bitbang_work looks at speed_hz, not max_speed_hz. So, I come back to
> > the same problem. Somehow speed_hz must be set in order to make bitbang_work
> > call setup_transfer, yet the only place that seems to happen is in spidev.
> sounds like the bitbang SPI bus driver is broken. if speed_hz is 0,
> then the bus driver should fall back to the max_speed_hz from the spi
I just looked at that code, and didn't see any obvious issue.
It relies on initial setup to be correct, and then restores it
after any per-transfer override.
Maybe the problem is that the OF-to-SPI linkage is still borked.
Is it ensuring spi_setup() was called at device setup time?
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