RE: [PATCH v2] media: nxp: imx8-isi: Add virtual channel support

From: G.N. Zhou (OSS)

Date: Wed Mar 25 2026 - 01:51:35 EST

Hi Laurent,

Thanks for your review.

> -----Original Message-----
> From: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> Sent: Friday, March 20, 2026 6:47 AM
> To: G.N. Zhou (OSS) <guoniu.zhou@xxxxxxxxxxx>
> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>; Frank Li
> <frank.li@xxxxxxx>; Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>; Pengutronix
> Kernel Team <kernel@xxxxxxxxxxxxxx>; Fabio Estevam
> <festevam@xxxxxxxxx>; linux-media@xxxxxxxxxxxxxxx; imx@xxxxxxxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; G.N. Zhou
> <guoniu.zhou@xxxxxxx>
> Subject: Re: [PATCH v2] media: nxp: imx8-isi: Add virtual channel support
>
> Hi Guoniu,
>
> Thank you for the patch.
>
> On Tue, Mar 10, 2026 at 02:53:10PM +0800, Guoniu Zhou wrote:
> > From: Guoniu Zhou <guoniu.zhou@xxxxxxx>
> >
> > Add virtual channel support for ISI driver.
>
> You can drop this line, it duplicates the subject line.
>
> > The ISI supports different numbers of virtual channels depending on
> > the platform. i.MX95 supports 8 virtual channels, and i.MX8QXP/QM
> > support 4 virtual channels. They are used in multiple camera use
> > cases, such as surround view. Other platforms (such as
> > i.MX8MN/8MP/8ULP/93/91) don't support virtual channels, and the VC_ID
> bits are marked as read-only.
> >
> > Reviewed-by: Frank Li <Frank.Li@xxxxxxx>
> > Signed-off-by: Guoniu Zhou <guoniu.zhou@xxxxxxx>
> > ---
> > Changes in v2:
> > - Add Rb tag from Frank Li
> > - Fix typo in comment(s/support/supports/)
> > - Update commit log to include more details about ISI virtual channel support
> > on different platform
> > - Include bitfield.h file to fix following build error
> > drivers/media/platform/nxp/imx8-isi/imx8-isi-regs.h:23:65: error:
> > implicit declaration of function ‘FIELD_PREP’
> > [-Wimplicit-function-declaration]
> > - Link to v1:
> > https://lore.kernel.org/r/20260309-isi_vc-v1-1-fd0b8035d1cd@xxxxxxx
> >
> > Changes in v1:
> > - Depends on
> > https://lore.kernel.org/linux-media/20251105-isi_imx95-v3-2-3987533cca
> > 1c@xxxxxxx/
> > ---
> > .../media/platform/nxp/imx8-isi/imx8-isi-core.h | 3 ++
> > drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c | 4 +-
> > .../media/platform/nxp/imx8-isi/imx8-isi-pipe.c | 43
> ++++++++++++++++++++++
> > .../media/platform/nxp/imx8-isi/imx8-isi-regs.h | 6 +--
> > 4 files changed, 52 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.h
> > b/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.h
> > index
> >
> 3cbd35305af0f8026c4f76b5eb5d0864f8e36dc3..11a5e395792f11752c44d738
> 18c8
> > 25f2f175aa1d 100644
> > --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.h
> > +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-core.h
> > @@ -256,6 +256,9 @@ struct mxc_isi_pipe {
> > u8 acquired_res;
> > u8 chained_res;
> > bool chained;
> > +
> > + /* Virtual channel ID for the ISI channel */
> > + u8 vc;
> > };
> >
> > struct mxc_isi_m2m {
> > diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c
> > b/drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c
> > index
> >
> 0187d4ab97e8e28fca9013f6864a094e08f2c570..2babb8573227de9e1aa36d9
> a39be
> > 41b286cf0c57 100644
> > --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c
> > +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c
> > @@ -338,7 +338,9 @@ static void mxc_isi_channel_set_control(struct
> mxc_isi_pipe *pipe,
> > } else {
> > val |= CHNL_CTRL_SRC_TYPE(CHNL_CTRL_SRC_TYPE_DEVICE);
> > val |= CHNL_CTRL_SRC_INPUT(input);
> > - val |= CHNL_CTRL_MIPI_VC_ID(0); /* FIXME: For CSI-2 only */
> > + val |= CHNL_CTRL_MIPI_VC_ID(pipe->vc);
>
> You're not addressing the FIXME comment, so it should be kept (or ideally
> addressed :-)).

Ok, will add it back.

>
> > + /* Platform like i.MX95, ISI supports 8 virtual channels */
> > + val |= CHNL_CTRL_VC_ID_1(pipe->vc >> 2);
>
> This should be done for i.MX95 only. You also need to clear the bit above in the
> function just after reading CHNL_CTRL (for i.MX95 only as well), otherwise
> switching between different virtual channels won't work.

Yes, you're right. Will fix it in next version.

>
> > }
> >
> > mxc_isi_write(pipe, CHNL_CTRL, val); diff --git
> > a/drivers/media/platform/nxp/imx8-isi/imx8-isi-pipe.c
> > b/drivers/media/platform/nxp/imx8-isi/imx8-isi-pipe.c
> > index
> >
> a41c51dd9ce0f2eeb779e9aa2461593b0d635f41..cc4348ea6006ee19243aae3
> abceb
> > 235d00beea4d 100644
> > --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-pipe.c
> > +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-pipe.c
> > @@ -232,6 +232,45 @@ static inline struct mxc_isi_pipe *to_isi_pipe(struct
> v4l2_subdev *sd)
> > return container_of(sd, struct mxc_isi_pipe, sd); }
> >
> > +static int mxc_isi_get_vc(struct mxc_isi_pipe *pipe) {
> > + struct mxc_isi_crossbar *xbar = &pipe->isi->crossbar;
> > + struct device *dev = pipe->isi->dev;
> > + struct v4l2_mbus_frame_desc source_fd;
> > + struct v4l2_mbus_frame_desc_entry *entry = NULL;
> > + unsigned int i;
> > + int ret;
> > +
> > + ret = v4l2_subdev_call(&xbar->sd, pad, get_frame_desc,
> > + xbar->num_sinks + pipe->id, &source_fd);
>
> I don't see the xbar implementing get_frame_desc(). Am I missing a
> dependency ?

Good catch, thank you.

The xbar get_frame_desc() implementation was developed separately and I
mistakenly didn't include it in this series. You're not missing anything -
it's my error in patch organization.

I will include it in next version to make this series self-contained and complete.

>
> > + if (ret < 0) {
> > + dev_err(dev, "Failed to get source frame desc from pad %u\n",
> > + xbar->num_sinks + pipe->id);
> > + return ret;
> > + }
> > +
> > + for (i = 0; i < source_fd.num_entries; i++) {
> > + if (source_fd.entry[i].stream == 0) {
> > + entry = &source_fd.entry[i];
> > + break;
> > + }
> > + }
> > +
> > + if (!entry) {
> > + dev_err(dev, "Failed to find stream from source frame desc\n");
> > + return -EPIPE;
> > + }
> > +
> > + if (entry->bus.csi2.vc >= pipe->isi->pdata->num_channels) {
> > + dev_err(dev, "Virtual channel(%d) out of range\n",
> > + entry->bus.csi2.vc);
> > + return -EINVAL;
> > + }
> > +
> > + pipe->vc = entry->bus.csi2.vc;
> > + return 0;
> > +}
> > +
> > int mxc_isi_pipe_enable(struct mxc_isi_pipe *pipe) {
> > struct mxc_isi_crossbar *xbar = &pipe->isi->crossbar; @@ -280,6
> > +319,10 @@ int mxc_isi_pipe_enable(struct mxc_isi_pipe *pipe)
> >
> > v4l2_subdev_unlock_state(state);
> >
> > + ret = mxc_isi_get_vc(pipe);
> > + if (ret)
> > + return ret;
> > +
> > /* Configure the ISI channel. */
> > mxc_isi_channel_config(pipe, input, &in_size, &scale, &crop,
> > sink_info->encoding, src_info->encoding); diff --git
> > a/drivers/media/platform/nxp/imx8-isi/imx8-isi-regs.h
> > b/drivers/media/platform/nxp/imx8-isi/imx8-isi-regs.h
> > index
> >
> 1b65eccdf0da4bbc3a77c91e06fccc35d6c7e022..a4036da72f0057265e991087
> f21b
> > c079bd6c6573 100644
> > --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-regs.h
> > +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-regs.h
> > @@ -6,6 +6,7 @@
> > #ifndef __IMX8_ISI_REGS_H__
> > #define __IMX8_ISI_REGS_H__
> >
> > +#include <linux/bitfield.h>
> > #include <linux/bits.h>
> >
> > /* ISI Registers Define */
> > @@ -19,9 +20,8 @@
> > #define CHNL_CTRL_CHAIN_BUF_NO_CHAIN 0
> > #define CHNL_CTRL_CHAIN_BUF_2_CHAIN 1
> > #define CHNL_CTRL_SW_RST BIT(24)
> > -#define CHNL_CTRL_BLANK_PXL(n) ((n) <<
> 16)
>
> I'm tempted to keep this, in case we'll need to set it later. We can add a
> comment to indicate the field is only valid on i.MX8QM and i.MX8QXP:
>
> #define CHNL_CTRL_BLANK_PXL(n) ((n) <<
> 16) /* i.MX8{QM,QXP} */
>
> or
>
> #define CHNL_CTRL_BLANK_PXL(n)
> FIELD_PREP(GENMASK(23, 16), (n)) /* i.MX8{QM,QXP} */
>
> > -#define CHNL_CTRL_BLANK_PXL_MASK
> GENMASK(23, 16)
> > -#define CHNL_CTRL_MIPI_VC_ID(n) ((n) <<
> 6)
> > +#define CHNL_CTRL_VC_ID_1(n)
> FIELD_PREP(BIT(16), (n))
>
> Please also add a comment to indicate the field is valid on i.MX95 only.
>
> #define CHNL_CTRL_VC_ID_1(n)
> FIELD_PREP(BIT(16), (n)) /* i.MX95 */
>

Sounds good. I will add a comment in next version to clarify this.

> > +#define CHNL_CTRL_MIPI_VC_ID(n)
> FIELD_PREP(GENMASK(7, 6), (n))
> > #define CHNL_CTRL_MIPI_VC_ID_MASK
> GENMASK(7, 6)
> > #define CHNL_CTRL_SRC_TYPE(n) ((n) <<
> 4)
> > #define CHNL_CTRL_SRC_TYPE_MASK BIT(4)
> >
> > ---
> > base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
> > change-id: 20260309-isi_vc-285fd815140e
> > prerequisite-patch-id: 6f139a1d54fa3e0632db9b8a736ae27037c5f45a
>
> --
> Regards,
>
> Laurent Pinchart