From: Ming Qian ming.qian@oss.nxp.com
[ Upstream commit fd5b6cd730676940df63b0970bb1ba30bca1aac3 ]
As the first frame in "repeat-mode" is the pattern, the pattern done interrupt is ignored by the driver. With small resolution bitstreams, the interrupts might fire too quickly and hardware combine two irqs to once because irq handle have latency. Thus the driver might miss the frame decode done interrupt from the first actual frame.
In order to avoid the driver wait for the frame done interrupt that has been combined to the pattern done interrupt and been ignored, driver will check the curr_desc and slot_status registers to figure out if the decoding of actual frame is finished or not.
Firstly we check the curr_desc register, - if it is still pointing to the pattern descriptor, the second actual frame is not started, we can wait for its frame-done interrupt. - if the curr_desc has pointed to the frame descriptor, then we check the ongoing bit of slot_status register. - if the ongoing bit is set to 1, the decoding of the actual frame is not finished, we can wait for its frame-done interrupt. - if the ongoing bit is set to 0, the decoding of the actual frame is finished, we can't wait for the second interrupt, but mark it as done.
But there is still a small problem, that the curr_desc and slot_status registers are not synchronous. curr_desc is updated when the next_descpt_ptr is loaded, but the ongoing bit of slot_status is set after the 32 bytes descriptor is loaded, there will be a short time interval in between, which may cause fake false. Consider read register is quite slow compared with IP read 32byte from memory, read twice slot_status can avoid this situation.
Signed-off-by: Ming Qian ming.qian@oss.nxp.com Reviewed-by: Frank Li Frank.Li@nxp.com Signed-off-by: Nicolas Dufresne nicolas.dufresne@collabora.com Signed-off-by: Hans Verkuil hverkuil@xs4all.nl Signed-off-by: Sasha Levin sashal@kernel.org ---
Based on my analysis of both the commit message and code changes, here is my determination: **YES** This commit should be backported to stable kernel trees for the following reasons: 1. **Fixes a real bug causing driver hangs**: The commit addresses a specific issue where the driver can wait indefinitely for an interrupt that has already been combined with a previous ignored interrupt. This causes the driver to hang, making the hardware unusable for motion-JPEG decoding with small resolution bitstreams. 2. **Clear bug fix with minimal changes**: The fix is targeted and minimal - it adds one new function (`mxc_dec_is_ongoing()`) and modifies one condition in the IRQ handler. The changes are well-contained within the imx-jpeg driver with no impact on other subsystems. 3. **Hardware-specific race condition**: The commit addresses a hardware behavior where interrupts can be combined when they fire too quickly. This is a real issue that affects users of the i.MX8 JPEG hardware decoder, particularly when processing small resolution motion-JPEG streams. 4. **No architectural changes**: The fix doesn't introduce any new features or change the driver's architecture. It simply adds additional state checking to handle a specific hardware race condition. 5. **Low regression risk**: The changes are defensive - they add additional checks before proceeding rather than changing existing behavior. The worst case would be that the new checks might not catch all edge cases, but they won't break existing working scenarios. 6. **Similar to other backported commits**: Looking at the similar commits marked as "YES" for backporting (like "media: imx-jpeg: Disable slot interrupt when frame done"), this follows the same pattern of fixing specific hardware issues that cause system problems. The commit specifically fixes a condition where the driver becomes stuck waiting for an interrupt that will never come, which is exactly the kind of bug that stable kernels should fix to ensure reliable operation of hardware.
.../media/platform/nxp/imx-jpeg/mxc-jpeg-hw.h | 1 + .../media/platform/nxp/imx-jpeg/mxc-jpeg.c | 31 ++++++++++++++++++- 2 files changed, 31 insertions(+), 1 deletion(-)
diff --git a/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg-hw.h b/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg-hw.h index d579c804b0479..adb93e977be91 100644 --- a/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg-hw.h +++ b/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg-hw.h @@ -89,6 +89,7 @@ /* SLOT_STATUS fields for slots 0..3 */ #define SLOT_STATUS_FRMDONE (0x1 << 3) #define SLOT_STATUS_ENC_CONFIG_ERR (0x1 << 8) +#define SLOT_STATUS_ONGOING (0x1 << 31)
/* SLOT_IRQ_EN fields TBD */
diff --git a/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c b/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c index 1221b309a9163..72b43abfaf903 100644 --- a/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c +++ b/drivers/media/platform/nxp/imx-jpeg/mxc-jpeg.c @@ -877,6 +877,34 @@ static u32 mxc_jpeg_get_plane_size(struct mxc_jpeg_q_data *q_data, u32 plane_no) return size; }
+static bool mxc_dec_is_ongoing(struct mxc_jpeg_ctx *ctx) +{ + struct mxc_jpeg_dev *jpeg = ctx->mxc_jpeg; + u32 curr_desc; + u32 slot_status; + + curr_desc = readl(jpeg->base_reg + MXC_SLOT_OFFSET(ctx->slot, SLOT_CUR_DESCPT_PTR)); + if (curr_desc == jpeg->slot_data.cfg_desc_handle) + return true; + + slot_status = readl(jpeg->base_reg + MXC_SLOT_OFFSET(ctx->slot, SLOT_STATUS)); + if (slot_status & SLOT_STATUS_ONGOING) + return true; + + /* + * The curr_desc register is updated when next_descpt_ptr is loaded, + * the ongoing bit of slot_status is set when the 32 bytes descriptor is loaded. + * So there will be a short time interval in between, which may cause fake false. + * Consider read register is quite slow compared with IP read 32byte from memory, + * read twice slot_status can avoid this situation. + */ + slot_status = readl(jpeg->base_reg + MXC_SLOT_OFFSET(ctx->slot, SLOT_STATUS)); + if (slot_status & SLOT_STATUS_ONGOING) + return true; + + return false; +} + static irqreturn_t mxc_jpeg_dec_irq(int irq, void *priv) { struct mxc_jpeg_dev *jpeg = priv; @@ -946,7 +974,8 @@ static irqreturn_t mxc_jpeg_dec_irq(int irq, void *priv) mxc_jpeg_enc_mode_go(dev, reg, mxc_jpeg_is_extended_sequential(q_data->fmt)); goto job_unlock; } - if (jpeg->mode == MXC_JPEG_DECODE && jpeg_src_buf->dht_needed) { + if (jpeg->mode == MXC_JPEG_DECODE && jpeg_src_buf->dht_needed && + mxc_dec_is_ongoing(ctx)) { jpeg_src_buf->dht_needed = false; dev_dbg(dev, "Decoder DHT cfg finished. Start decoding...\n"); goto job_unlock;