Re: [PATCH 00/10] Raspberry Pi SPI speedups

[Lukas Wunner <lukas@xxxxxxxxx>]

On Sun, Aug 11, 2019 at 09:50:17PM +0200, Stefan Wahren wrote:
> Am 03.08.19 um 12:10 schrieb Lukas Wunner:
> > So far the BCM2835 SPI driver cannot cope with TX-only and RX-only
> > transfers (rx_buf or tx_buf is NULL) when using DMA:  It relies on
> > the SPI core to convert them to full-duplex transfers by allocating
> > and DMA-mapping a dummy rx_buf or tx_buf.  This costs performance.
> >
> > Resolve by pre-allocating reusable DMA descriptors which cyclically
> > clear the RX FIFO (for TX-only transfers) or zero-fill the TX FIFO
> > (for RX-only transfers).  Patch [07/10] provides some numbers for
> > the achieved latency improvement and CPU time reduction with an
> > SPI Ethernet controller.  SPI displays should see a similar speedup.
> > I've also made an effort to reduce peripheral and memory bus accesses.
> 
> i know the BCM2711 / Raspberry Pi 4 isn't upstreamed yet, but this
> series hasn't been tested with RPi 4?

No, I only have the CM1 and CM3 at my disposal for testing,
the series seemed to work fine on both.

Thanks,

Lukas