e143364b4c
spi-bcm2835 can handle >64kB buffers now so there is no need to check ->max_dma_len. The tinydrm_spi_max_transfer_size() max_len argument is not used by any callers, so not needed. Then we have the spi_max module parameter. It was added because staging/fbtft has support for it and there was a report that someone used it to set a small buffer size to avoid popping on a USB soundcard on a Raspberry Pi. In hindsight it shouldn't have been added, I should have waited for it to become a problem first. I don't know it anyone is actually using it, but since tinydrm_spi_transfer() is being moved to mipi-dbi, I'm taking the opportunity to remove it. I'll add it back to mipi-dbi if someone complains. With that out of the way, spi_max_transfer_size() can be used instead. The chosen 16kB buffer size for Type C Option 1 (9-bit) interface is somewhat arbitrary, but a bigger buffer will have a miniscule impact on transfer speed, so it's probably fine. Acked-by: Sam Ravnborg <sam@ravnborg.org> Signed-off-by: Noralf Trønnes <noralf@tronnes.org> Link: https://patchwork.freedesktop.org/patch/msgid/20190719155916.62465-6-noralf@tronnes.org
102 lines
2.2 KiB
C
102 lines
2.2 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Copyright (C) 2016 Noralf Trønnes
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*/
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#include <linux/backlight.h>
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#include <linux/dma-buf.h>
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#include <linux/module.h>
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#include <linux/pm.h>
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#include <linux/spi/spi.h>
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#include <linux/swab.h>
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#include <drm/drm_device.h>
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#include <drm/drm_drv.h>
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#include <drm/drm_fourcc.h>
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#include <drm/drm_framebuffer.h>
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#include <drm/drm_print.h>
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#include <drm/drm_rect.h>
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#include <drm/tinydrm/tinydrm-helpers.h>
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#if IS_ENABLED(CONFIG_SPI)
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/**
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* tinydrm_spi_transfer - SPI transfer helper
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* @spi: SPI device
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* @speed_hz: Override speed (optional)
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* @header: Optional header transfer
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* @bpw: Bits per word
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* @buf: Buffer to transfer
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* @len: Buffer length
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*
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* This SPI transfer helper breaks up the transfer of @buf into chunks which
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* the SPI master driver can handle. If the machine is Little Endian and the
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* SPI master driver doesn't support 16 bits per word, it swaps the bytes and
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* does a 8-bit transfer.
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* If @header is set, it is prepended to each SPI message.
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*
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* Returns:
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* Zero on success, negative error code on failure.
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*/
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int tinydrm_spi_transfer(struct spi_device *spi, u32 speed_hz,
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struct spi_transfer *header, u8 bpw, const void *buf,
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size_t len)
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{
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size_t max_chunk = spi_max_transfer_size(spi);
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struct spi_transfer tr = {
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.bits_per_word = bpw,
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.speed_hz = speed_hz,
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};
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struct spi_message m;
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u16 *swap_buf = NULL;
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size_t chunk;
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int ret = 0;
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if (WARN_ON_ONCE(bpw != 8 && bpw != 16))
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return -EINVAL;
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if (bpw == 16 && !spi_is_bpw_supported(spi, 16)) {
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tr.bits_per_word = 8;
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if (tinydrm_machine_little_endian()) {
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swap_buf = kmalloc(min(len, max_chunk), GFP_KERNEL);
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if (!swap_buf)
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return -ENOMEM;
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}
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}
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spi_message_init(&m);
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if (header)
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spi_message_add_tail(header, &m);
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spi_message_add_tail(&tr, &m);
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while (len) {
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chunk = min(len, max_chunk);
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tr.tx_buf = buf;
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tr.len = chunk;
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if (swap_buf) {
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const u16 *buf16 = buf;
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unsigned int i;
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for (i = 0; i < chunk / 2; i++)
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swap_buf[i] = swab16(buf16[i]);
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tr.tx_buf = swap_buf;
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}
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buf += chunk;
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len -= chunk;
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ret = spi_sync(spi, &m);
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if (ret)
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return ret;
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}
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return 0;
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}
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EXPORT_SYMBOL(tinydrm_spi_transfer);
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#endif /* CONFIG_SPI */
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MODULE_LICENSE("GPL");
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