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Subject[PATCH] media: platform: mtk-mdp: Fix mdp_ipi_comm structure alignment
Date
The mdp_ipi_comm structure defines a command that is either
PROCESS (start processing) or DEINIT (destroy instance); we
are using this one to send PROCESS or DEINIT commands from Linux
to an MDP instance through a VPU write but, while the first wants
us to stay 4-bytes aligned, the VPU instead requires an 8-bytes
data alignment.

Keeping in mind that these commands are executed immediately
after sending them (hence not chained with others before the
VPU/MDP "actually" start executing), it is fine to simply add
a padding of 4 bytes to this structure: this keeps the same
performance as before, as we're still stack-allocating it,
while avoiding hackery inside of mtk-vpu to ensure alignment
bringing a definitely bigger performance impact.

Fixes: c8eb2d7e8202 ("[media] media: Add Mediatek MDP Driver")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
---

This patch has been tested on Acer Chromebook R 13 (MT8173 Elm) on Debian Sid.

This is an alternative solution to the mtk-vpu approach, found here:
https://lore.kernel.org/all/20210920170408.1561-1-dafna.hirschfeld@collabora.com

drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h | 2 ++
1 file changed, 2 insertions(+)

diff --git a/drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h b/drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h
index 2cb8cecb3077..b810c96695c8 100644
--- a/drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h
+++ b/drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h
@@ -40,12 +40,14 @@ struct mdp_ipi_init {
* @ipi_id : IPI_MDP
* @ap_inst : AP mtk_mdp_vpu address
* @vpu_inst_addr : VPU MDP instance address
+ * @padding : Alignment padding
*/
struct mdp_ipi_comm {
uint32_t msg_id;
uint32_t ipi_id;
uint64_t ap_inst;
uint32_t vpu_inst_addr;
+ uint32_t padding;
};

/**
--
2.35.1
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