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57 lines
2.2 KiB
Diff
57 lines
2.2 KiB
Diff
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From 5631d65a09fe2249d22fad0985c25dc776b41808 Mon Sep 17 00:00:00 2001
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From: Naushir Patuck <naush@raspberrypi.com>
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Date: Fri, 2 Sep 2022 08:35:35 +0100
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Subject: [PATCH] media: bcm2835-unicam: Fix for possible dummy buffer
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overrun
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The Unicam hardware has been observed to cause a buffer overrun when using the
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dummy buffer as a circular buffer. The conditions that cause the overrun are not
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fully known, but it seems to occur when the memory bus is heavily loaded.
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To avoid the overrun, program the hardware with a buffer size of 0 when using
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the dummy buffer. This will cause overrun into the allocated dummy buffer, but
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avoid out of bounds writes.
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Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
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---
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drivers/media/platform/bcm2835/bcm2835-unicam.c | 14 ++++++++------
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1 file changed, 8 insertions(+), 6 deletions(-)
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--- a/drivers/media/platform/bcm2835/bcm2835-unicam.c
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+++ b/drivers/media/platform/bcm2835/bcm2835-unicam.c
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@@ -126,8 +126,11 @@ MODULE_PARM_DESC(media_controller, "Use
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#define UNICAM_EMBEDDED_SIZE 16384
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/*
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- * Size of the dummy buffer. Can be any size really, but the DMA
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- * allocation works in units of page sizes.
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+ * Size of the dummy buffer allocation.
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+ *
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+ * Due to a HW bug causing buffer overruns in circular buffer mode under certain
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+ * (not yet fully known) conditions, the dummy buffer allocation is set to a
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+ * a single page size, but the hardware gets programmed with a buffer size of 0.
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*/
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#define DUMMY_BUF_SIZE (PAGE_SIZE)
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@@ -843,8 +846,7 @@ static void unicam_schedule_dummy_buffer
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unicam_dbg(3, dev, "Scheduling dummy buffer for node %d\n",
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node->pad_id);
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- unicam_wr_dma_addr(dev, node->dummy_buf_dma_addr, DUMMY_BUF_SIZE,
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- node->pad_id);
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+ unicam_wr_dma_addr(dev, node->dummy_buf_dma_addr, 0, node->pad_id);
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node->next_frm = NULL;
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}
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@@ -2662,8 +2664,8 @@ static void unicam_stop_streaming(struct
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* This is only really needed if the embedded data pad is
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* disabled before the image pad.
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*/
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- unicam_wr_dma_addr(dev, node->dummy_buf_dma_addr,
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- DUMMY_BUF_SIZE, METADATA_PAD);
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+ unicam_wr_dma_addr(dev, node->dummy_buf_dma_addr, 0,
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+ METADATA_PAD);
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}
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/* Clear all queued buffers for the node */
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