2022-03-08 11:04:54

by Yunhao Tian

Subject: [PATCH] drm/mipi-dbi: Fix max_chunk calculation in spi_transfer

In __spi_validate, there's a validation that no partial transfers
are accepted (xfer->len % w_size must be zero). When
max_chunk is not a multiple of bpw (e.g.max_chunk = 65535,
bpw = 16), the transfer will be rejected.

This patch clamps max_chunk to the word size, preventing
the transfer from being rejected.

Signed-off-by: Yunhao Tian <[email protected]>
---
drivers/gpu/drm/drm_mipi_dbi.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
index 71b646c4131f..440dc9fec6cc 100644
--- a/drivers/gpu/drm/drm_mipi_dbi.c
+++ b/drivers/gpu/drm/drm_mipi_dbi.c
@@ -1182,6 +1182,15 @@ int mipi_dbi_spi_transfer(struct spi_device *spi, u32 speed_hz,
struct spi_message m;
size_t chunk;
int ret;
+ int w_size;
+
+ if (bpw <= 8)
+ w_size = 1;
+ else if (bpw <= 16)
+ w_size = 2;
+ else
+ w_size = 4;
+ max_chunk -= (max_chunk % w_size);

spi_message_init_with_transfers(&m, &tr, 1);

--
2.25.1

2022-04-16 09:03:04

by Noralf Trønnes

Subject: Re: [PATCH] drm/mipi-dbi: Fix max_chunk calculation in spi_transfer

Den 08.03.2022 02.56, skrev Yunhao Tian:
> In __spi_validate, there's a validation that no partial transfers
> are accepted (xfer->len % w_size must be zero). When
> max_chunk is not a multiple of bpw (e.g.max_chunk = 65535,
> bpw = 16), the transfer will be rejected.
>
> This patch clamps max_chunk to the word size, preventing

I think align is a better word here than clamp.

> the transfer from being rejected.
>
> Signed-off-by: Yunhao Tian <[email protected]>
> ---
> drivers/gpu/drm/drm_mipi_dbi.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
> index 71b646c4131f..440dc9fec6cc 100644
> --- a/drivers/gpu/drm/drm_mipi_dbi.c
> +++ b/drivers/gpu/drm/drm_mipi_dbi.c
> @@ -1182,6 +1182,15 @@ int mipi_dbi_spi_transfer(struct spi_device *spi, u32 speed_hz,
> struct spi_message m;
> size_t chunk;
> int ret;
> + int w_size;
> +
> + if (bpw <= 8)
> + w_size = 1;
> + else if (bpw <= 16)
> + w_size = 2;
> + else
> + w_size = 4;
> + max_chunk -= (max_chunk % w_size);

mipi_dbi_spi_transfer() is only called with bpw= 8 or 16, so I think
this can be simplified to: max_chunk = ALIGN_DOWN(max_chunk, 2);
We might shorten the max transfer by one byte when bpw=8, but that
doesn't matter. A short comment explaining why we need this would be nice.

Please add a fixes tag so the patch is backported to the stable kernels:

Fixes: d23d4d4dac01 ("drm/tinydrm: Move tinydrm_spi_transfer()")

Noralf.

>
> spi_message_init_with_transfers(&m, &tr, 1);
>