Re: [PATCH 6/7] drm/udl: Untangle .get_modes() and .detect_ctx()

[Thomas Zimmermann <tzimmermann@xxxxxxx>]

Hi

Am 05.04.24 um 09:09 schrieb Jani Nikula:
> On Thu, 04 Apr 2024, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote:
> > Provide separate implementations of .get_modes() and .detect_ctx()
> > from struct drm_connector. Switch to struct drm_edid.
> >
> > Udl's .detect() helper used to fetch the EDID from the adapter and the
> > .get_modes() helper provided display modes from the data. Switching to
> > the new helpers around struct drm_edid separates both from each other. The
> > .get_modes() helper now fetches the EDID by itself and the .detect_ctx()
> > helper only tests for its presence.
> FWIW, this is what I had for UDL in my branch of various drm_edid
> conversions:
>
> https://gitlab.freedesktop.org/jani/linux/-/commit/c6357a778182eff7acfb1eb832809377f799edaf
>
> You seem to claim that there's inherent value in separating detect and
> get_modes hooks from each other, with the former not reading the full
> EDID.

Yes. If udl stores the EDID in struct udl_connector and later uses it in 
get_modes, the detect always has to run before get_modes. That logic is 
deeply hidden in the DRM probe helpers. So in any case, I want get_modes 
to read the EDID by itself.

In detect or detect_ctx, using drm_edid_read_custom() might do 
unnecessary USB transfers. Maybe not a problem per-se, but udl is 
already pushing the limits of its USB 2 bus. And the read function also 
leaves a warning about the all-zero EDID data in the kernel log every 
few seconds. Probably from [1].

[1] 
https://elixir.bootlin.com/linux/v6.8/source/drivers/gpu/drm/drm_edid.c#L2389

> If you do read the full EDID using drm_edid_read_custom() in detect,
> you'll get more validation of the EDID for free, with no need to add
> extra drm edid interfaces for probing with optional header validation.
>
> Some drivers need to use EDID contents for the purpose of detect
> too. Perhaps not UDL.
>
> Also let's look at the override/firmware EDID mechanism. If you have a
> completely broken EDID, the newly added drm_edid_probe_custom() will
> never detect connected. You'll need to use connector forcing, even if
> the DDC probe would have been enough.

The EDID probe helper can take this into account. If it's just the code 
at [2], it looks simple enough to re-use.

[2] 
https://elixir.bootlin.com/linux/v6.8/source/drivers/gpu/drm/drm_edid.c#L2373

Best regards
Thomas

> BR,
> Jani.
>
> > The patch does a number of things to implement this.
> >
> > - Move udl_get_edid_block() to udl_edid.c and rename it to
> > udl_read_edid_block(). Then use the helper to implement probing in
> > udl_probe_edid() and reading in udl_edid_read(). Both udl helpers
> > are build on top of DRM helpers.
> >
> > - Replace the existing code in .get_modes() and .detect() with udl's
> > new EDID helpers. The new code behaves like DRM's similar DDC-based
> > helpers. Instead of .detect(), udl now implements .detect_ctx().
> >
> > - Remove the edid data from struct udl_connector. The field cached
> > the EDID data between calls to .detect() and .get_modes(), but is now
> > unused.
> >
> > Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
> > ---
> >   drivers/gpu/drm/udl/Makefile      |  1 +
> >   drivers/gpu/drm/udl/udl_drv.h     |  2 -
> >   drivers/gpu/drm/udl/udl_edid.c    | 67 +++++++++++++++++++++++
> >   drivers/gpu/drm/udl/udl_edid.h    | 15 ++++++
> >   drivers/gpu/drm/udl/udl_modeset.c | 90 +++++++------------------------
> >   5 files changed, 102 insertions(+), 73 deletions(-)
> >   create mode 100644 drivers/gpu/drm/udl/udl_edid.c
> >   create mode 100644 drivers/gpu/drm/udl/udl_edid.h
> >
> > diff --git a/drivers/gpu/drm/udl/Makefile b/drivers/gpu/drm/udl/Makefile
> > index 00690741db376..43d69a16af183 100644
> > --- a/drivers/gpu/drm/udl/Makefile
> > +++ b/drivers/gpu/drm/udl/Makefile
> > @@ -2,6 +2,7 @@
> >   
> >   udl-y := \
> >   	udl_drv.o \
> > +	udl_edid.o \
> >   	udl_main.o \
> >   	udl_modeset.o \
> >   	udl_transfer.o
> > diff --git a/drivers/gpu/drm/udl/udl_drv.h b/drivers/gpu/drm/udl/udl_drv.h
> > index 282ebd6c02fda..f112cfb270f31 100644
> > --- a/drivers/gpu/drm/udl/udl_drv.h
> > +++ b/drivers/gpu/drm/udl/udl_drv.h
> > @@ -51,8 +51,6 @@ struct urb_list {
> >   
> >   struct udl_connector {
> >   	struct drm_connector connector;
> > -	/* last udl_detect edid */
> > -	struct edid *edid;
> >   };
> >   
> >   static inline struct udl_connector *to_udl_connector(struct drm_connector *connector)
> > diff --git a/drivers/gpu/drm/udl/udl_edid.c b/drivers/gpu/drm/udl/udl_edid.c
> > new file mode 100644
> > index 0000000000000..caa9641996e92
> > --- /dev/null
> > +++ b/drivers/gpu/drm/udl/udl_edid.c
> > @@ -0,0 +1,67 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +
> > +#include <drm/drm_drv.h>
> > +#include <drm/drm_edid.h>
> > +
> > +#include "udl_drv.h"
> > +#include "udl_edid.h"
> > +
> > +static int udl_read_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
> > +{
> > +	struct udl_device *udl = data;
> > +	struct drm_device *dev = &udl->drm;
> > +	struct usb_device *udev = udl_to_usb_device(udl);
> > +	u8 *read_buff;
> > +	int idx, ret;
> > +	size_t i;
> > +
> > +	read_buff = kmalloc(2, GFP_KERNEL);
> > +	if (!read_buff)
> > +		return -ENOMEM;
> > +
> > +	if (!drm_dev_enter(dev, &idx)) {
> > +		ret = -ENODEV;
> > +		goto err_kfree;
> > +	}
> > +
> > +	for (i = 0; i < len; i++) {
> > +		int bval = (i + block * EDID_LENGTH) << 8;
> > +
> > +		ret = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
> > +				      0x02, (0x80 | (0x02 << 5)), bval,
> > +				      0xA1, read_buff, 2, USB_CTRL_GET_TIMEOUT);
> > +		if (ret < 0) {
> > +			drm_err(dev, "Read EDID byte %zu failed err %x\n", i, ret);
> > +			goto err_drm_dev_exit;
> > +		} else if (ret < 1) {
> > +			ret = -EIO;
> > +			drm_err(dev, "Read EDID byte %zu failed\n", i);
> > +			goto err_drm_dev_exit;
> > +		}
> > +
> > +		buf[i] = read_buff[1];
> > +	}
> > +
> > +	drm_dev_exit(idx);
> > +	kfree(read_buff);
> > +
> > +	return 0;
> > +
> > +err_drm_dev_exit:
> > +	drm_dev_exit(idx);
> > +err_kfree:
> > +	kfree(read_buff);
> > +	return ret;
> > +}
> > +
> > +bool udl_probe_edid(struct udl_device *udl)
> > +{
> > +	return drm_edid_probe_custom(udl_read_edid_block, udl, true);
> > +}
> > +
> > +const struct drm_edid *udl_edid_read(struct drm_connector *connector)
> > +{
> > +	struct udl_device *udl = to_udl(connector->dev);
> > +
> > +	return drm_edid_read_custom(connector, udl_read_edid_block, udl);
> > +}
> > diff --git a/drivers/gpu/drm/udl/udl_edid.h b/drivers/gpu/drm/udl/udl_edid.h
> > new file mode 100644
> > index 0000000000000..fe15ff3752b7d
> > --- /dev/null
> > +++ b/drivers/gpu/drm/udl/udl_edid.h
> > @@ -0,0 +1,15 @@
> > +/* SPDX-License-Identifier: GPL-2.0-only */
> > +
> > +#ifndef UDL_EDID_H
> > +#define UDL_EDID_H
> > +
> > +#include <linux/types.h>
> > +
> > +struct drm_connector;
> > +struct drm_edid;
> > +struct udl_device;
> > +
> > +bool udl_probe_edid(struct udl_device *udl);
> > +const struct drm_edid *udl_edid_read(struct drm_connector *connector);
> > +
> > +#endif
> > diff --git a/drivers/gpu/drm/udl/udl_modeset.c b/drivers/gpu/drm/udl/udl_modeset.c
> > index 3df9fc38388b4..4236ce57f5945 100644
> > --- a/drivers/gpu/drm/udl/udl_modeset.c
> > +++ b/drivers/gpu/drm/udl/udl_modeset.c
> > @@ -25,6 +25,7 @@
> >   #include <drm/drm_vblank.h>
> >   
> >   #include "udl_drv.h"
> > +#include "udl_edid.h"
> >   #include "udl_proto.h"
> >   
> >   /*
> > @@ -415,97 +416,44 @@ static const struct drm_encoder_funcs udl_encoder_funcs = {
> >   
> >   static int udl_connector_helper_get_modes(struct drm_connector *connector)
> >   {
> > -	struct udl_connector *udl_connector = to_udl_connector(connector);
> > +	const struct drm_edid *drm_edid;
> > +	int count;
> >   
> > -	drm_connector_update_edid_property(connector, udl_connector->edid);
> > -	if (udl_connector->edid)
> > -		return drm_add_edid_modes(connector, udl_connector->edid);
> > +	drm_edid = udl_edid_read(connector);
> > +	drm_edid_connector_update(connector, drm_edid);
> > +	count = drm_edid_connector_add_modes(connector);
> > +	drm_edid_free(drm_edid);
> >   
> > -	return 0;
> > +	return count;
> >   }
> >   
> > -static const struct drm_connector_helper_funcs udl_connector_helper_funcs = {
> > -	.get_modes = udl_connector_helper_get_modes,
> > -};
> > -
> > -static int udl_get_edid_block(void *data, u8 *buf, unsigned int block, size_t len)
> > +static int udl_connector_helper_detect_ctx(struct drm_connector *connector,
> > +					   struct drm_modeset_acquire_ctx *ctx,
> > +					   bool force)
> >   {
> > -	struct udl_device *udl = data;
> > -	struct drm_device *dev = &udl->drm;
> > -	struct usb_device *udev = udl_to_usb_device(udl);
> > -	u8 *read_buff;
> > -	int idx, ret;
> > -	size_t i;
> > -
> > -	read_buff = kmalloc(2, GFP_KERNEL);
> > -	if (!read_buff)
> > -		return -ENOMEM;
> > +	struct udl_device *udl = to_udl(connector->dev);
> >   
> > -	if (!drm_dev_enter(dev, &idx)) {
> > -		ret = -ENODEV;
> > -		goto err_kfree;
> > -	}
> > -
> > -	for (i = 0; i < len; i++) {
> > -		int bval = (i + block * EDID_LENGTH) << 8;
> > -
> > -		ret = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
> > -				      0x02, (0x80 | (0x02 << 5)), bval,
> > -				      0xA1, read_buff, 2, USB_CTRL_GET_TIMEOUT);
> > -		if (ret < 0) {
> > -			drm_err(dev, "Read EDID byte %zu failed err %x\n", i, ret);
> > -			goto err_drm_dev_exit;
> > -		} else if (ret < 1) {
> > -			ret = -EIO;
> > -			drm_err(dev, "Read EDID byte %zu failed\n", i);
> > -			goto err_drm_dev_exit;
> > -		}
> > -
> > -		buf[i] = read_buff[1];
> > -	}
> > +	if (udl_probe_edid(udl))
> > +		return connector_status_connected;
> >   
> > -	drm_dev_exit(idx);
> > -	kfree(read_buff);
> > -
> > -	return 0;
> > -
> > -err_drm_dev_exit:
> > -	drm_dev_exit(idx);
> > -err_kfree:
> > -	kfree(read_buff);
> > -	return ret;
> > +	return connector_status_disconnected;
> >   }
> >   
> > -static enum drm_connector_status udl_connector_detect(struct drm_connector *connector, bool force)
> > -{
> > -	struct drm_device *dev = connector->dev;
> > -	struct udl_device *udl = to_udl(dev);
> > -	struct udl_connector *udl_connector = to_udl_connector(connector);
> > -	enum drm_connector_status status = connector_status_disconnected;
> > -
> > -	/* cleanup previous EDID */
> > -	kfree(udl_connector->edid);
> > -	udl_connector->edid = NULL;
> > -
> > -	udl_connector->edid = drm_do_get_edid(connector, udl_get_edid_block, udl);
> > -	if (udl_connector->edid)
> > -		status = connector_status_connected;
> > -
> > -	return status;
> > -}
> > +static const struct drm_connector_helper_funcs udl_connector_helper_funcs = {
> > +	.get_modes = udl_connector_helper_get_modes,
> > +	.detect_ctx = udl_connector_helper_detect_ctx,
> > +};
> >   
> >   static void udl_connector_destroy(struct drm_connector *connector)
> >   {
> >   	struct udl_connector *udl_connector = to_udl_connector(connector);
> >   
> >   	drm_connector_cleanup(connector);
> > -	kfree(udl_connector->edid);
> >   	kfree(udl_connector);
> >   }
> >   
> >   static const struct drm_connector_funcs udl_connector_funcs = {
> >   	.reset = drm_atomic_helper_connector_reset,
> > -	.detect = udl_connector_detect,
> >   	.fill_modes = drm_helper_probe_single_connector_modes,
> >   	.destroy = udl_connector_destroy,
> >   	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,

--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)