Den 25.02.2018 14.19, skrev Lukas Wunner:
[cc += linux-rpi-ker...@lists.infradead.org]
On Sat, Feb 24, 2018 at 06:15:59PM +0000, Meghana Madhyastha wrote:
I've added bcm2835_spi_transfer_one_message in spi-bcm2835. This calls
spi_split_transfers_maxsize to split large chunks for spi dma transfers.
I then removed chunk splitting in the tinydrm spi helper (as now the core
is handling the chunk splitting). However, although the SPI HW should be
able to accomodate up to 65535 bytes for dma transfers, the splitting of
chunks to 65535 bytes results in a dma transfer time out error. However,
when the chunks are split to < 64 bytes it seems to work fine.
Hm, that is really odd, how did you test this exactly, what did you
use as SPI slave? It contradicts our own experience, we're using
Micrel KSZ8851 Ethernet chips as SPI slave on spi0 of a BCM2837
and can send/receive messages via DMA to the tune of several hundred
bytes without any issues. In fact, for messages < 96 bytes, DMA is
not used at all, so you've probably been using interrupt mode,
see the BCM2835_SPI_DMA_MIN_LENGTH macro in spi-bcm2835.c.
Meghana,
I suggest using modetest with page flipping to check that you don't
regress performance wise:
$ ./libdrm/tests/modetest/modetest -M mi0283qt -s 28:320x240@RG16 -v
setting mode 320x240-0Hz@RG16 on connectors 28, crtc 30
freq: 29.88Hz
freq: 29.96Hz
freq: 29.99Hz
^C
Noralf.
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