Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
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>,
        Sam Ravnborg <sam@ravnborg.org>,
        David Lechner <david@lechnology.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2] drm/mipi-dbi: align max_chunk to 2 in spi_transfer
Date:   Tue, 10 May 2022 11:02:19 +0800
Message-Id: <20220510030219.2486687-1-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 aligns max_chunk to 2 bytes (the maximum value of bpw is 16),
so that no partial transfer will occur.

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

Signed-off-by: Yunhao Tian <t123yh.xyz@gmail.com>
---
 drivers/gpu/drm/drm_mipi_dbi.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
index 71b646c4131f..00d470ff071d 100644
--- a/drivers/gpu/drm/drm_mipi_dbi.c
+++ b/drivers/gpu/drm/drm_mipi_dbi.c
@@ -1183,6 +1183,13 @@ int mipi_dbi_spi_transfer(struct spi_device *spi, u32 speed_hz,
 	size_t chunk;
 	int ret;
 
+	/* In __spi_validate, there's a validation that no partial transfers
+	 * are accepted (xfer->len % w_size must be zero).
+	 * Here we align max_chunk to multiple of 2 (16bits),
+	 * to prevent transfers from being rejected.
+	 */
+	max_chunk = ALIGN_DOWN(max_chunk, 2);
+
 	spi_message_init_with_transfers(&m, &tr, 1);
 
 	while (len) {
-- 
2.25.1