Hi Brown,
Nice to get feedback from you!
In current source code of spi_transfer_one_message(),
1420 bool keep_cs = false;
1488 if (xfer->cs_change) {
1489 if (list_is_last(&xfer->transfer_list,
1490 &msg->transfers)) {
1491 keep_cs = true;
1492 } else {
1493 spi_set_cs(msg->spi, false, false);
1494 _spi_transfer_cs_change_delay(msg, xfer);
1495 spi_set_cs(msg->spi, true, false);
1496 }
1497 }
1502 out:
1503 if (ret != 0 || !keep_cs)
1504 spi_set_cs(msg->spi, false, false);
if the last xfer->cs_change is true, keep_cs will be true, and it will
not call spi_set_cs() to set CS to false. Do you mean to keep CS enabled
in this case?
On 2/9/22 9:40 PM, Mark Brown wrote:
On Wed, Feb 09, 2022 at 06:00:42PM +0800, Yun Zhou wrote:
If there are 2 slaves or more on a spi bus, e.g. A and B, we processed a
transfer to A, the CS will be selected for A whose 'last_cs_enable' will
be recorded to true at the same time. Then we processed a transfer to B,
the CS will be switched to B. And then if we transmit data to A again, it
will not enable CS back to A because 'last_cs_enable' is true.
In addition, if CS is not disabled, Some controllers in automatic
transmission state will receive unpredictable data, such as Cadence SPI
controller.
This sounds like you've got an issue with mixing devices with and
without CS_HIGH - that is probably broken but...
out:
- if (ret != 0 || !keep_cs)
- spi_set_cs(msg->spi, false, false);
+ spi_set_cs(msg->spi, false, false);
...this will obviously break cs_change support, clearly that's not OK.
The last_cs_high should be moved to the device.
I do not think it will break cs_change support. In my understanding,
cs_change indicates whether or not change CS after an xfer completed.
But at present if the last xfer->cs_change is true, we will not change
CS to disabled state. Is this the result we want? I'm confused.
I look forward to your help and explanation.
Regards,
Yun
