Den 13.03.2022 15.10, skrev trix@xxxxxxxxxx:
> From: Tom Rix <trix@xxxxxxxxxx>
>
> repaper_spi_transfer() allocates a single byte
> for the spi header and then another buffer for
> the payload. Combine the allocs into a single
> buffer with offsets. To simplify the offsets
> put the header after the payload.
>
> Signed-off-by: Tom Rix <trix@xxxxxxxxxx>
> ---
> drivers/gpu/drm/tiny/repaper.c | 40 ++++++++++------------------------
> 1 file changed, 12 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/gpu/drm/tiny/repaper.c b/drivers/gpu/drm/tiny/repaper.c
> index 37b6bb90e46e1..22a6732f35a01 100644
> --- a/drivers/gpu/drm/tiny/repaper.c
> +++ b/drivers/gpu/drm/tiny/repaper.c
> @@ -100,50 +100,34 @@ static inline struct repaper_epd *drm_to_epd(struct drm_device *drm)
> static int repaper_spi_transfer(struct spi_device *spi, u8 header,
> const void *tx, void *rx, size_t len)
> {
> - void *txbuf = NULL, *rxbuf = NULL;
> struct spi_transfer tr[2] = {};
> - u8 *headerbuf;
> + u8 *buf;
> int ret;
>
> - headerbuf = kmalloc(1, GFP_KERNEL);
> - if (!headerbuf)
> + buf = kmalloc(1 + len, GFP_KERNEL);
> + if (!buf)
> return -ENOMEM;
>
> - headerbuf[0] = header;
> - tr[0].tx_buf = headerbuf;
> + buf[len] = header;
> + tr[0].tx_buf = &buf[len];
I don't think this will work since the buffer is used directly for DMA
on some platforms[1] so the buffers need to be at the correct alignment
for that to work. For this reason I think it's better to leave this
as-is since we know the kmalloc buffers will always be useable for DMA
and the code is also easy to read and understand instead of calculating
offsets.
[1] tinydrm/mipi-dbi: Use dma-safe buffers for all SPI transfers
(a89bfc5d9a07)
Noralf.
> tr[0].len = 1;
>
> - /* Stack allocated tx? */
> - if (tx && len <= 32) {
> - txbuf = kmemdup(tx, len, GFP_KERNEL);
> - if (!txbuf) {
> - ret = -ENOMEM;
> - goto out_free;
> - }
> + if (tx) {
> + memcpy(buf, tx, len);
> + tr[1].tx_buf = buf;
> }
>
> - if (rx) {
> - rxbuf = kmalloc(len, GFP_KERNEL);
> - if (!rxbuf) {
> - ret = -ENOMEM;
> - goto out_free;
> - }
> - }
> + if (rx)
> + tr[1].rx_buf = buf;
>
> - tr[1].tx_buf = txbuf ? txbuf : tx;
> - tr[1].rx_buf = rxbuf;
> tr[1].len = len;
>
> ndelay(80);
> ret = spi_sync_transfer(spi, tr, 2);
> if (rx && !ret)
> - memcpy(rx, rxbuf, len);
> -
> -out_free:
> - kfree(headerbuf);
> - kfree(txbuf);
> - kfree(rxbuf);
> + memcpy(rx, buf, len);
>
> + kfree(buf);
> return ret;
> }
>
