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From:   Yunhao Tian <t123yh.xyz@gmail.com>
To:     =?UTF-8?q?Noralf=20Tr=C3=B8nnes?= <noralf@tronnes.org>
Cc:     Yunhao Tian <t123yh.xyz@gmail.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: [PATCH] drm/mipi-dbi: Fix max_chunk calculation in spi_transfer
Date:   Tue,  8 Mar 2022 09:56:11 +0800
Message-Id: <20220308015611.3007395-1-t123yh.xyz@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

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 <t123yh.xyz@gmail.com>
---
 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