Hi Daniel, On Thu, Aug 4, 2016 at 8:16 PM, Daniel Palmer <danieruru@xxxxxxxxx> wrote: > On 5 August 2016 at 02:56, Chris Brandt <Chris.Brandt@xxxxxxxxxxx> wrote: >> From: linux-renesas-soc-owner@xxxxxxxxxxxxxxx >> [mailto:linux-renesas-soc-owner@xxxxxxxxxxxxxxx] On Behalf Of Daniel Palmer >> I got DMA working on the RZ/A1H and started to notice this: >> >> spi_master spi0: receive timeout >> >> What seems to be happening is that there is a DMA transfer for the SPI bus >> happening so the interrupts are masked. A small transfer that is smaller >> than the fifo size comes along so __rspi_can_dma returns false and a PIO >> transfer is started but the interrupt to say it's finished is handled by the >> DMA controller so the spi driver never sees that it finished. Making >> __rspi_can_dma always return true makes the problem go away. > I think I have actually worked this one out. I was blaming the SPI > driver incorrectly. As a person having worked on the rspi driver, I'm happy to hear that ;-) > The DMA driver (Hacked up version from the BSP with DT support) was > never resetting the register (DMARS) that causes the SPI interrupts to > be routed there instead. > So after a DMA transfer PIO never worked again. Oops... > I'm not sure it's actually any faster with DMA as there are massive > delays between each byte being transmitted. That's a shame, as on R-Car Gen2 it made a big difference when using DMA for single SPI transfers, cfr. commit 4f12b5e529e4ff274eb478ec1c2ef41358ed9577 Author: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> Date: Mon Jun 2 15:38:17 2014 +0200 spi: rspi: Add DMA support for QSPI on R-Car Gen2 Enable DMA support for QSPI on R-Car Gen2, for Single, Dual, and Quad SPI Transfers. Performance figures for reading from a QSPI FLASH driven at 24.375 MHz on r8a7791/koelsch: - Single: 1.1 Mbps PIO, 23 Mbps DMA - Dual : 12.7 Mbps PIO, 48 Mbps DMA - Quad : 13 Mbps PIO, 70 Mbps DMA 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
