[PATCH v5 0/4] serial: sh-sci: Fix fallback to PIO on DMA failure

[Geert Uytterhoeven <geert+renesas@glider.be>]

	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 case 1, which is the only one
that does not work yet in v5.0-rc1.

Changes compared to v4:
  - Drop patches to fix case 2, whch have been applied in v5.0-rc1,
  - Add patches to extract common helpers and make naming more
    consistent,
  - Call new helpers sci_dma_rx_chan_invalidate() and
    sci_dma_rx_reenable_irq() instead of open-coding.

Changes compared to v3:
  - Let sci_submit_rx() return -EAGAIN instead of -1 on failure,
  - Check for negative error in sci_submit_rx() caller.

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-v5 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: Extract sci_dma_rx_chan_invalidate()
  serial: sh-sci: Extract sci_dma_rx_reenable_irq()
  serial: sh-sci: Fix fallback to PIO in sci_dma_rx_complete()
  serial: sh-sci: Make RX/TX DMA function names consistent

 drivers/tty/serial/sh-sci.c | 71 ++++++++++++++++++++++---------------
 1 file changed, 43 insertions(+), 28 deletions(-)

-- 
2.17.1

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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