CV-Bowen opened a new pull request, #21069:
URL: https://github.com/apache/nuttx/pull/21069
## Summary
`spi_transfer()` always de-selects the device at the end of a sequence,
so a caller cannot express "keep CS asserted for the next sequence". A
protocol backend needs that: virtio-spi carries a `cs_change` flag, and
its false value means the next request continues on the same chip select
without a new select/deselect cycle.
Add `spi_sequence_s.keepcs`. With it set, the trailing `SPI_SELECT()` is
skipped; an aborted sequence (`ret < 0`) still de-selects, so CS is never
left asserted after an error. Honor `HWFEAT_FORCE_CS_ACTIVE/INACTIVE_AFTER_
TRANSFER` in the per-transfer de-select decision as well.
## Impact
- `struct spi_sequence_s` gains a byte. Nothing in tree initializes it
positionally (`regmap_spi.c` and `spitool` assign fields by name), and a
zero-initialized sequence keeps the current behavior, so existing
callers are unaffected.
- No Kconfig change.
- The first user will be the vhost-spi backend, which is not upstream yet.
## Testing
Host: Ubuntu 22.04.5 LTS x86_64, QEMU version 10.2.1, sim: cc (Ubuntu
13.1.0-8ubuntu1~22.04) 13.1.0, qemu-armv8a: aarch64-none-elf-gcc (Arm GNU
Toolchain 12.2.Rel1 (Build arm-12.24)) 12.2.1 20221205
A sequence that keeps CS leaves it asserted, one that does not still
de-asserts it. Checked on `sim:nsh` with a small app that builds its own
`spi_dev_s` whose `select` records the state and calls `spi_transfer()`
directly, so no board SPI controller is involved:
```
nsh> keepcstest
keepcs=0 cs=0
keepcs=1 round 0 cs=1 selects=2
keepcs=1 round 1 cs=1 selects=4
```
`cs=0` for the first sequence is the unchanged behavior; `cs=1` after
each `keepcs=1` sequence shows CS carried over, and `selects` counts the
two `select(true)` calls per sequence (one before the loop, one inside
it).
<details><summary>Test app (not part of this PR)</summary>
```c
int main(int argc, FAR char *argv[])
{
FAR struct keepcs_dev_s *priv = &g_keepcs_dev;
struct spi_sequence_s seq;
int i;
memset(&seq, 0, sizeof(seq));
seq.dev = SPIDEV_NONE(0);
seq.ntrans = 1;
seq.trans = &g_trans;
seq.frequency = 1000000;
seq.keepcs = 0;
spi_transfer(&priv->dev, &seq);
printf("keepcs=0 cs=%d\n", priv->selected ? 1 : 0);
priv->selected = false;
priv->selects = 0;
seq.keepcs = 1;
for (i = 0; i < 2; i++)
{
spi_transfer(&priv->dev, &seq);
printf("keepcs=1 round %d cs=%d selects=%d\n",
i, priv->selected ? 1 : 0, priv->selects);
}
return 0;
}
```
</details>
Baseline (`test.sh`, cases: baseline.yaml):
- host: Ubuntu 22.04.5 LTS x86_64, QEMU version 10.2.1, sim: cc (Ubuntu
13.1.0-8ubuntu1~22.04) 13.1.0, qemu-armv8a: aarch64-none-elf-gcc (Arm GNU
Toolchain 12.2.Rel1 (Build arm-12.24)) 12.2.1 20221205
- tested: nuttx 848c63288a9 apps 5f1100d02
- qemu-armv8a built with test-only overlay: disabled LIBC_ENVPATH
BINFMT_CHECKEXEC
- sim:rpserver + sim:rpproxy: PASS
- [x] `uname -a` (server)
- [x] `rpmsg dump all` (server)
- [x] `rpmsg ping all 10 1024 3 0` (server)
- [x] `uname -a` (proxy)
- [x] `rpmsg ping all 10 1024 3 0` (proxy)
- [x] `mount -t rpmsgfs -o cpu=server,fs=/proc /sp` (proxy)
- [x] `cat /sp/version` (proxy)
- [x] `rpmsg dump all` (proxy)
- qemu-armv8a:rpserver + qemu-armv8a:rpproxy: PASS
- [x] `uname -a` (server)
- [x] `uname -a` (proxy)
- [x] `rpmsg dump all` (server)
- [x] `rpmsg ping all 10 1024 3 0` (server)
- [x] `rpmsg ping all 10 1024 3 0` (proxy)
- [x] `mount -t rpmsgfs -o cpu=server,fs=/proc /sp` (proxy)
- [x] `cat /sp/version` (proxy)
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