can: tcan4x5x: rework SPI access
This patch reworks the SPI access and fixes several probems: - tcan4x5x_regmap_gather_write(), tcan4x5x_regmap_read(): Do not place variable "addr" on stack and use it as buffer for SPI transfer. Buffers for SPI transfers must be allocated from DMA save memory. - tcan4x5x_regmap_gather_write(), tcan4x5x_regmap_read(): Halfe number of SPI transfers by using a single buffer + memcpy(). This improves the performance, especially on SPI controllers, which use interrupt based transfers. - Use "8" bits per word, not "32". This makes it possible to use this driver on SoCs like the Raspberry Pi, which SPI host controller drivers only support 8 bits per word. Note: this breaks half duplex only controllers. Support for them will be re-added in the next patch. Reviewed-by: Dan Murphy <dmurphy@ti.com> Tested-by: Sean Nyekjaer <sean@geanix.com> Link: https://lore.kernel.org/r/20201215231746.1132907-16-mkl@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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