[PATCH v4] drm/omap: dsi: avoid sending bta sync all the time in writes

[PATCH v4] drm/omap: dsi: avoid sending bta sync all the time in writes

[Andreas Kemnade]

Some chips need configuration commands to be sent first, before they can
send data. TC358762 for example needs PPI_LPTXTIMECNT configured
and PPI_STARTPPI set to 1 to be able to transmit anything. To be able to
configure such chips, do not send bta sync during writes if no acks are
requested. Instead just wait for the packet to be sent to avoid FIFO
overflows. There might be more to do about acks, but there seem to be
virtually no users of that flag.

This came to light when fiddling with the Epson Moverio BT-200 display
which consists of 2 TC358762 bridges with SPI funneled through
to the unknown display chip. With that patch the bridge can be accessed,
Reading back registers works, when the above-mentioned registers are set.

In Command-Mode update, there was a nop sent, apparently the most
relevant part was the bta sync to actually force low power mode.

Video mode panel at OMAP4 (BT-200) and video mode at OMAP5 was tested.

Fixes: e70965386353e ("drm/omap: dsi: simplify write function")
Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
---
Changes in v4:
- wait on completition on all packets (was limited to long packets only,
  because I had the wrong impression that there is no confirmation on
  these)
- Link to v3: https://patch.msgid.link/20260628-vm-upstr-v3-1-9e9add93378b@kemnade.info

Changes in v3:

- Link to v2: https://patch.msgid.link/20260529-vm-upstr-v2-1-24c30671719f@kernel.org
- fix things mentioned by claude here:
  https://lore.gitlab.freedesktop.org/drm-ai-reviews/review-patch1-20260529-vm-upstr-v2-1-24c30671719f@kernel.org/
  - fix typos
  - register ISR before sending packet
  - check for RX_FIFO_NOT_EMPTY also in for short packets

Changes in v2:
- fix commandmode update, need bta sync there
- do not wait on short packets
- Link to v1: https://patch.msgid.link/20260528-vm-upstr-v1-1-fb93ef8cbe47@kernel.org

To: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
To: Maxime Ripard <mripard@kernel.org>
To: Thomas Zimmermann <tzimmermann@suse.de>
To: David Airlie <airlied@gmail.com>
To: Simona Vetter <simona@ffwll.ch>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Sebastian Reichel <sebastian.reichel@collabora.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
---
 drivers/gpu/drm/omapdrm/dss/dsi.c | 53 ++++++++++++++++++---------------------
 1 file changed, 24 insertions(+), 29 deletions(-)

diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
index 27fe7bca9e2c..3f22929c36e2 100644
--- a/drivers/gpu/drm/omapdrm/dss/dsi.c
+++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
@@ -2194,28 +2194,38 @@ static int dsi_vc_send_null(struct dsi_data *dsi, int vc, int channel)
 static int dsi_vc_write_common(struct omap_dss_device *dssdev, int vc,
 			       const struct mipi_dsi_msg *msg)
 {
+	DECLARE_COMPLETION_ONSTACK(completion);
 	struct dsi_data *dsi = to_dsi_data(dssdev);
 	int r;
 
+	/* wait for IRQ for packet transmission confirmation */
+	r = dsi_register_isr_vc(dsi, vc, dsi_completion_handler,
+				&completion, DSI_VC_IRQ_PACKET_SENT);
+	if (r)
+		return r;
+
 	if (mipi_dsi_packet_format_is_short(msg->type))
 		r = dsi_vc_send_short(dsi, vc, msg);
 	else
 		r = dsi_vc_send_long(dsi, vc, msg);
 
-	if (r < 0)
+	if ((!r) && wait_for_completion_timeout(&completion,
+				msecs_to_jiffies(500)) == 0)
+		r = -EIO;
+
+	dsi_unregister_isr_vc(dsi, vc, dsi_completion_handler,
+			      &completion, DSI_VC_IRQ_PACKET_SENT);
+	if (r)
 		return r;
 
-	/*
-	 * TODO: we do not always have to do the BTA sync, for example
-	 * we can improve performance by setting the update window
-	 * information without sending BTA sync between the commands.
-	 * In that case we can return early.
-	 */
+	/* TODO: find out if more needs to be done for MIPI_DSI_MSG_REQ_ACK */
 
-	r = dsi_vc_send_bta_sync(dssdev, vc);
-	if (r) {
-		DSSERR("bta sync failed\n");
-		return r;
+	if (msg->flags & MIPI_DSI_MSG_REQ_ACK) {
+		r = dsi_vc_send_bta_sync(dssdev, vc);
+		if (r) {
+			DSSERR("bta sync failed\n");
+			return r;
+		}
 	}
 
 	/* RX_FIFO_NOT_EMPTY */
@@ -3233,21 +3243,6 @@ static int _dsi_update(struct dsi_data *dsi)
 	return 0;
 }
 
-static int _dsi_send_nop(struct dsi_data *dsi, int vc, int channel)
-{
-	const u8 payload[] = { MIPI_DCS_NOP };
-	const struct mipi_dsi_msg msg = {
-		.channel = channel,
-		.type = MIPI_DSI_DCS_SHORT_WRITE,
-		.tx_len = 1,
-		.tx_buf = payload,
-	};
-
-	WARN_ON(!dsi_bus_is_locked(dsi));
-
-	return _omap_dsi_host_transfer(dsi, vc, &msg);
-}
-
 static int dsi_update_channel(struct omap_dss_device *dssdev, int vc)
 {
 	struct dsi_data *dsi = to_dsi_data(dssdev);
@@ -3268,13 +3263,13 @@ static int dsi_update_channel(struct omap_dss_device *dssdev, int vc)
 	DSSDBG("dsi_update_channel: %d", vc);
 
 	/*
-	 * Send NOP between the frames. If we don't send something here, the
+	 * Transition to LP here. If we don't send something here, the
 	 * updates stop working. This is probably related to DSI spec stating
 	 * that the DSI host should transition to LP at least once per frame.
 	 */
-	r = _dsi_send_nop(dsi, VC_CMD, dsi->dsidev->channel);
+	r = dsi_vc_send_bta_sync(dssdev, vc);
 	if (r < 0) {
-		DSSWARN("failed to send nop between frames: %d\n", r);
+		DSSWARN("failed to send bta sync between frames: %d\n", r);
 		goto err;
 	}
 

---
base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
change-id: 20260528-vm-upstr-c8e7634ebf56

Best regards,
--  
Andreas Kemnade <andreas@kemnade.info>

Re: [PATCH v4] drm/omap: dsi: avoid sending bta sync all the time in writes

[Ivaylo Dimitrov]

Hi,
With this version of the patch I see:

[  102.760894] DSI: omapdss DSI error: Framedone not received for 250ms!
[  303.860321] DSI: omapdss DSI error: Framedone not received for 250ms!
[  307.071624] DSI: omapdss DSI error: Framedone not received for 250ms!
[  307.360626] DSI: omapdss DSI error: Framedone not received for 250ms!
[  307.671142] DSI: omapdss DSI error: Framedone not received for 250ms!
[  308.660339] DSI: omapdss DSI error: Framedone not received for 250ms!
[  308.961059] DSI: omapdss DSI error: Framedone not received for 250ms!
[  313.191314] DSI: omapdss DSI error: Framedone not received for 250ms!
[  313.700378] DSI: omapdss DSI error: Failed to set dsi_if_enable to 0
[  313.980346] DSI: omapdss DSI error: Framedone not received for 250ms!
[  314.791564] DSI: omapdss DSI error: Framedone not received for 250ms!
[  315.090362] DSI: omapdss DSI error: Framedone not received for 250ms!
[  322.850952] DSI: omapdss DSI error: Framedone not received for 250ms!
[  323.111175] DSI: omapdss DSI error: Framedone not received for 250ms!

while scrolling the (hildon)desktop on droid4, so I would say the change 
broke command mode.

Regards,
Ivo

On 29.06.26 г. 18:50 ч., Andreas Kemnade wrote:
> Some chips need configuration commands to be sent first, before they can
> send data. TC358762 for example needs PPI_LPTXTIMECNT configured
> and PPI_STARTPPI set to 1 to be able to transmit anything. To be able to
> configure such chips, do not send bta sync during writes if no acks are
> requested. Instead just wait for the packet to be sent to avoid FIFO
> overflows. There might be more to do about acks, but there seem to be
> virtually no users of that flag.
> 
> This came to light when fiddling with the Epson Moverio BT-200 display
> which consists of 2 TC358762 bridges with SPI funneled through
> to the unknown display chip. With that patch the bridge can be accessed,
> Reading back registers works, when the above-mentioned registers are set.
> 
> In Command-Mode update, there was a nop sent, apparently the most
> relevant part was the bta sync to actually force low power mode.
> 
> Video mode panel at OMAP4 (BT-200) and video mode at OMAP5 was tested.
> 
> Fixes: e70965386353e ("drm/omap: dsi: simplify write function")
> Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
> ---
> Changes in v4:
> - wait on completition on all packets (was limited to long packets only,
>    because I had the wrong impression that there is no confirmation on
>    these)
> - Link to v3: https://patch.msgid.link/20260628-vm-upstr-v3-1-9e9add93378b@kemnade.info
> 
> Changes in v3:
> 
> - Link to v2: https://patch.msgid.link/20260529-vm-upstr-v2-1-24c30671719f@kernel.org
> - fix things mentioned by claude here:
>    https://lore.gitlab.freedesktop.org/drm-ai-reviews/review-patch1-20260529-vm-upstr-v2-1-24c30671719f@kernel.org/
>    - fix typos
>    - register ISR before sending packet
>    - check for RX_FIFO_NOT_EMPTY also in for short packets
> 
> Changes in v2:
> - fix commandmode update, need bta sync there
> - do not wait on short packets
> - Link to v1: https://patch.msgid.link/20260528-vm-upstr-v1-1-fb93ef8cbe47@kernel.org
> 
> To: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
> To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> To: Maxime Ripard <mripard@kernel.org>
> To: Thomas Zimmermann <tzimmermann@suse.de>
> To: David Airlie <airlied@gmail.com>
> To: Simona Vetter <simona@ffwll.ch>
> To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> To: Sebastian Reichel <sebastian.reichel@collabora.com>
> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> Cc: dri-devel@lists.freedesktop.org
> Cc: linux-kernel@vger.kernel.org
> ---
>   drivers/gpu/drm/omapdrm/dss/dsi.c | 53 ++++++++++++++++++---------------------
>   1 file changed, 24 insertions(+), 29 deletions(-)
> 
> diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
> index 27fe7bca9e2c..3f22929c36e2 100644
> --- a/drivers/gpu/drm/omapdrm/dss/dsi.c
> +++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
> @@ -2194,28 +2194,38 @@ static int dsi_vc_send_null(struct dsi_data *dsi, int vc, int channel)
>   static int dsi_vc_write_common(struct omap_dss_device *dssdev, int vc,
>   			       const struct mipi_dsi_msg *msg)
>   {
> +	DECLARE_COMPLETION_ONSTACK(completion);
>   	struct dsi_data *dsi = to_dsi_data(dssdev);
>   	int r;
>   
> +	/* wait for IRQ for packet transmission confirmation */
> +	r = dsi_register_isr_vc(dsi, vc, dsi_completion_handler,
> +				&completion, DSI_VC_IRQ_PACKET_SENT);
> +	if (r)
> +		return r;
> +
>   	if (mipi_dsi_packet_format_is_short(msg->type))
>   		r = dsi_vc_send_short(dsi, vc, msg);
>   	else
>   		r = dsi_vc_send_long(dsi, vc, msg);
>   
> -	if (r < 0)
> +	if ((!r) && wait_for_completion_timeout(&completion,
> +				msecs_to_jiffies(500)) == 0)
> +		r = -EIO;
> +
> +	dsi_unregister_isr_vc(dsi, vc, dsi_completion_handler,
> +			      &completion, DSI_VC_IRQ_PACKET_SENT);
> +	if (r)
>   		return r;
>   
> -	/*
> -	 * TODO: we do not always have to do the BTA sync, for example
> -	 * we can improve performance by setting the update window
> -	 * information without sending BTA sync between the commands.
> -	 * In that case we can return early.
> -	 */
> +	/* TODO: find out if more needs to be done for MIPI_DSI_MSG_REQ_ACK */
>   
> -	r = dsi_vc_send_bta_sync(dssdev, vc);
> -	if (r) {
> -		DSSERR("bta sync failed\n");
> -		return r;
> +	if (msg->flags & MIPI_DSI_MSG_REQ_ACK) {
> +		r = dsi_vc_send_bta_sync(dssdev, vc);
> +		if (r) {
> +			DSSERR("bta sync failed\n");
> +			return r;
> +		}
>   	}
>   
>   	/* RX_FIFO_NOT_EMPTY */
> @@ -3233,21 +3243,6 @@ static int _dsi_update(struct dsi_data *dsi)
>   	return 0;
>   }
>   
> -static int _dsi_send_nop(struct dsi_data *dsi, int vc, int channel)
> -{
> -	const u8 payload[] = { MIPI_DCS_NOP };
> -	const struct mipi_dsi_msg msg = {
> -		.channel = channel,
> -		.type = MIPI_DSI_DCS_SHORT_WRITE,
> -		.tx_len = 1,
> -		.tx_buf = payload,
> -	};
> -
> -	WARN_ON(!dsi_bus_is_locked(dsi));
> -
> -	return _omap_dsi_host_transfer(dsi, vc, &msg);
> -}
> -
>   static int dsi_update_channel(struct omap_dss_device *dssdev, int vc)
>   {
>   	struct dsi_data *dsi = to_dsi_data(dssdev);
> @@ -3268,13 +3263,13 @@ static int dsi_update_channel(struct omap_dss_device *dssdev, int vc)
>   	DSSDBG("dsi_update_channel: %d", vc);
>   
>   	/*
> -	 * Send NOP between the frames. If we don't send something here, the
> +	 * Transition to LP here. If we don't send something here, the
>   	 * updates stop working. This is probably related to DSI spec stating
>   	 * that the DSI host should transition to LP at least once per frame.
>   	 */
> -	r = _dsi_send_nop(dsi, VC_CMD, dsi->dsidev->channel);
> +	r = dsi_vc_send_bta_sync(dssdev, vc);
>   	if (r < 0) {
> -		DSSWARN("failed to send nop between frames: %d\n", r);
> +		DSSWARN("failed to send bta sync between frames: %d\n", r);
>   		goto err;
>   	}
>   
> 
> ---
> base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
> change-id: 20260528-vm-upstr-c8e7634ebf56
> 
> Best regards,
> --
> Andreas Kemnade <andreas@kemnade.info>
> 

Re: [PATCH v4] drm/omap: dsi: avoid sending bta sync all the time in writes

[Andreas Kemnade]

On Tue, 30 Jun 2026 08:42:57 +0300
Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com> wrote:

> Hi,
> With this version of the patch I see:
> 
> [  102.760894] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  303.860321] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  307.071624] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  307.360626] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  307.671142] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  308.660339] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  308.961059] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  313.191314] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  313.700378] DSI: omapdss DSI error: Failed to set dsi_if_enable to 0
> [  313.980346] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  314.791564] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  315.090362] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  322.850952] DSI: omapdss DSI error: Framedone not received for 250ms!
> [  323.111175] DSI: omapdss DSI error: Framedone not received for 250ms!
> 
> while scrolling the (hildon)desktop on droid4, so I would say the change 
> broke command mode.
> 
so let me summarize:
- sending initialisation commands to video mode panel: no problem visible in
  any case, theretical problems (not seen with the tested panels if sending too much data, fixed via v4.
- command mode display: no picture and error messages without any bta sync (patch version 1).
- working display with send_nop() replaced by simply sending bta_sync() and not
  waiting for PACKET_SENT irq for short packets (v2).
- partly working display (with v4), (always waiting for PACKET_SENT)

so there are some situations when waiting for a packet completition is harmful.
In your case these were only siutations when short packets were sent.
Do you have a more complete log of v4 boott?
In the log for v1 which is not accessible anymore, there were other 
more informative timeouts visible.

But maybe as a wild guess also based on Sasikhos AI reviews, maybe
this helps:

diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
index 3f22929c36e2..eb3cd0d23cae 100644
--- a/drivers/gpu/drm/omapdrm/dss/dsi.c
+++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
@@ -3267,7 +3267,7 @@ static int dsi_update_channel(struct omap_dss_device *dssdev, int vc)
 	 * updates stop working. This is probably related to DSI spec stating
 	 * that the DSI host should transition to LP at least once per frame.
 	 */
-	r = dsi_vc_send_bta_sync(dssdev, vc);
+	r = dsi_vc_send_bta_sync(dssdev, VC_CMD);
 	if (r < 0) {
 		DSSWARN("failed to send bta sync between frames: %d\n", r);
 		goto err;



Then the call is equal to the original one done via send_nnop.

Regards,
Andreas

Re: [PATCH v4] drm/omap: dsi: avoid sending bta sync all the time in writes

[Ivaylo Dimitrov]

On 7.07.26 г. 13:22 ч., Andreas Kemnade wrote:
> On Tue, 30 Jun 2026 08:42:57 +0300
> Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com> wrote:
> 
>> Hi,
>> With this version of the patch I see:
>>
>> [  102.760894] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  303.860321] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  307.071624] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  307.360626] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  307.671142] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  308.660339] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  308.961059] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  313.191314] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  313.700378] DSI: omapdss DSI error: Failed to set dsi_if_enable to 0
>> [  313.980346] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  314.791564] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  315.090362] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  322.850952] DSI: omapdss DSI error: Framedone not received for 250ms!
>> [  323.111175] DSI: omapdss DSI error: Framedone not received for 250ms!
>>
>> while scrolling the (hildon)desktop on droid4, so I would say the change
>> broke command mode.
>>
> so let me summarize:
> - sending initialisation commands to video mode panel: no problem visible in
>    any case, theretical problems (not seen with the tested panels if sending too much data, fixed via v4.
> - command mode display: no picture and error messages without any bta sync (patch version 1).
> - working display with send_nop() replaced by simply sending bta_sync() and not
>    waiting for PACKET_SENT irq for short packets (v2).
> - partly working display (with v4), (always waiting for PACKET_SENT)
> 
> so there are some situations when waiting for a packet completition is harmful.
> In your case these were only siutations when short packets were sent.
> Do you have a more complete log of v4 boott?
> In the log for v1 which is not accessible anymore, there were other
> more informative timeouts visible.
> 
> But maybe as a wild guess also based on Sasikhos AI reviews, maybe
> this helps:
> 
> diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
> index 3f22929c36e2..eb3cd0d23cae 100644
> --- a/drivers/gpu/drm/omapdrm/dss/dsi.c
> +++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
> @@ -3267,7 +3267,7 @@ static int dsi_update_channel(struct omap_dss_device *dssdev, int vc)
>   	 * updates stop working. This is probably related to DSI spec stating
>   	 * that the DSI host should transition to LP at least once per frame.
>   	 */
> -	r = dsi_vc_send_bta_sync(dssdev, vc);
> +	r = dsi_vc_send_bta_sync(dssdev, VC_CMD);
>   	if (r < 0) {
>   		DSSWARN("failed to send bta sync between frames: %d\n", r);
>   		goto err;
> 
> 
> 
> Then the call is equal to the original one done via send_nnop.
> 

With that change it seems to work properly, will keep that version of 
the driver for the time being.

> Regards,
> Andreas