Hi Greg, Jiri,
When submitting a DMA request fails, the sh-sci driver is supposed to
fall back to PIO. However, this never really worked due to various
reasons (sh-sci driver issues and dmaengine framework limitations).
There are three places where DMA submission can fail, and the driver
should fall back to PIO:
1. sci_dma_rx_complete(),
2. sci_submit_rx(),
3. work_fn_tx().
This patch series fixes fallback to PIO in the receive path (cases 1 and
2).
Fallback to PIO in the transmit path (case 3) already seems to work
fine.
Changes compared to v2:
- Add missing definition of "u16 scr" to sci_dma_rx_complete(),
- Move label handle_pio inside #ifdef to kill defined but not used
compiler warning when CONFIG_SERIAL_SH_SCI_DMA=n,
- Move call to dmaengine_terminate_async() in sci_dma_rx_complete()
inside the spinlock, for symmetry with sci_submit_rx(),
- Move the call sci_submit_rx() in sci_rx_interrupt() up, as it may
fail, rendering the modification of scr unused,
- Split in multiple patches,
- Drop RFC status.
Changes compared to v1:
- Fix fallback in sci_dma_rx_complete(),
- Fallback in the transmit path already works fine,
- Widen audience, but keep RFC.
This has been tested on r8a7791/koelsch, using SCIF1 on debug serial 1,
and SCIFA3 on EXIO-B, by introducing random failures in DMA submission
code. For testing, this series is also available in the
topic/scif-pio-fallback-v3 branch of my renesas-drivers git repository
at
git://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git.
Thanks!
Geert Uytterhoeven (4):
serial: sh-sci: Fix locking in sci_submit_rx()
serial: sh-sci: Fix crash in rx_timer_fn() on PIO fallback
serial: sh-sci: Resume PIO in sci_rx_interrupt() on DMA failure
serial: sh-sci: Fix fallback to PIO in sci_dma_rx_complete()
drivers/tty/serial/sh-sci.c | 39 +++++++++++++++++++++++++++----------
1 file changed, 29 insertions(+), 10 deletions(-)
--
2.17.1
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
