Linux-ACPI Archive on lore.kernel.org
 help / color / Atom feed
From: Tomasz Figa <tfiga@chromium.org>
To: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: linux-acpi@vger.kernel.org, "Mani,
	Rajmohan" <rajmohan.mani@intel.com>,
	Linux Media Mailing List <linux-media@vger.kernel.org>
Subject: Re: [PATCH 3/5] ov5670: Support probe whilst the device is off
Date: Fri, 7 Jun 2019 16:54:06 +0900
Message-ID: <CAAFQd5D+RZS0E6xpZ3v8gC5zerj5fd6b6YxcAS_TeWei6vGvUA@mail.gmail.com> (raw)
In-Reply-To: <20190605101535.4sydewuv656x6c2g@kekkonen.localdomain>

On Wed, Jun 5, 2019 at 7:15 PM Sakari Ailus
<sakari.ailus@linux.intel.com> wrote:
>
> Hi Tomasz,
>
> On Wed, Jun 05, 2019 at 04:07:52PM +0900, Tomasz Figa wrote:
> > Hi Sakari,
> >
> > On Fri, May 10, 2019 at 01:09:28PM +0300, Sakari Ailus wrote:
> > > Tell ACPI device PM code that the driver supports the device being powered
> > > off when the driver's probe function is entered.
> > >
> > > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > > ---
> > >  drivers/media/i2c/ov5670.c | 25 ++++++++++++++-----------
> > >  1 file changed, 14 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/drivers/media/i2c/ov5670.c b/drivers/media/i2c/ov5670.c
> > > index 041fcbb4eebdf..57e8b92f90e09 100644
> > > --- a/drivers/media/i2c/ov5670.c
> > > +++ b/drivers/media/i2c/ov5670.c
> > > @@ -2444,6 +2444,7 @@ static int ov5670_probe(struct i2c_client *client)
> > >     struct ov5670 *ov5670;
> > >     const char *err_msg;
> > >     u32 input_clk = 0;
> > > +   bool powered_off;
> > >     int ret;
> > >
> > >     device_property_read_u32(&client->dev, "clock-frequency", &input_clk);
> > > @@ -2460,11 +2461,14 @@ static int ov5670_probe(struct i2c_client *client)
> > >     /* Initialize subdev */
> > >     v4l2_i2c_subdev_init(&ov5670->sd, client, &ov5670_subdev_ops);
> > >
> > > -   /* Check module identity */
> > > -   ret = ov5670_identify_module(ov5670);
> > > -   if (ret) {
> > > -           err_msg = "ov5670_identify_module() error";
> > > -           goto error_print;
> > > +   powered_off = acpi_dev_powered_off_for_probe(&client->dev);
> > > +   if (!powered_off) {
> > > +           /* Check module identity */
> > > +           ret = ov5670_identify_module(ov5670);
> > > +           if (ret) {
> > > +                   err_msg = "ov5670_identify_module() error";
> > > +                   goto error_print;
> > > +           }
> > >     }
> >
> > I don't like the fact that we can't detect any hardware connection issue
> > here anymore and we would actually get some obscure failure when we
> > actually start streaming.
> >
> > Wouldn't it be possible to still keep this behavior of not powering on
> > the device at boot-up if no driver is bound and then have this driver
> > built as a module and loaded later when the camera is to be used for the
> > first time after the system boots?
>
> That'd be a way to work around this, but the downside would be that the
> user space would need to know not only which drivers to load, but also
> which drivers _not_ to load. The user space could obtain the former from
> the kernel but not the latter, it'd be system specific configuration.
>
> Moving the responsibility of loading the driver to user space would also
> not address figuring out whether the sensor is accessible through its
> control bus: you have to power it on to do that. In fact, if you want to be
> sure that the hardware is all right, you have to start streaming on the
> device first and that is not a part of a typical driver initialisation
> sequence. Just checking the sensor is accessible over I涎 is not enough.
>
> The proposed solution addresses the problem without user space changes.

I guess that makes sense indeed. If going this way, why not just move
all the hardware access from probe to streamon and avoid any
conditional checks at all?

Best regards,
Tomasz

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-10 10:09 [PATCH 0/5] Support running driver's probe for a device powered off Sakari Ailus
2019-05-10 10:09 ` [PATCH 1/5] ACPI: Enable driver and firmware hints to control power at probe time Sakari Ailus
2019-05-31  9:17   ` Rafael J. Wysocki
2019-06-05 12:07     ` Sakari Ailus
2019-05-10 10:09 ` [PATCH 2/5] ACPI: Add a convenience function to tell a device is suspended in probe Sakari Ailus
2019-05-10 10:09 ` [PATCH 3/5] ov5670: Support probe whilst the device is off Sakari Ailus
2019-06-05  7:07   ` Tomasz Figa
2019-06-05 10:15     ` Sakari Ailus
2019-06-07  7:54       ` Tomasz Figa [this message]
2019-08-26  8:38         ` Sakari Ailus
2019-08-26  9:21           ` Tomasz Figa
2019-05-10 10:09 ` [PATCH 4/5] media: i2c: imx319: Support probe while " Sakari Ailus
2019-05-10 10:09 ` [PATCH 5/5] at24: Support probing while off Sakari Ailus

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAAFQd5D+RZS0E6xpZ3v8gC5zerj5fd6b6YxcAS_TeWei6vGvUA@mail.gmail.com \
    --to=tfiga@chromium.org \
    --cc=linux-acpi@vger.kernel.org \
    --cc=linux-media@vger.kernel.org \
    --cc=rajmohan.mani@intel.com \
    --cc=sakari.ailus@linux.intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-ACPI Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-acpi/0 linux-acpi/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-acpi linux-acpi/ https://lore.kernel.org/linux-acpi \
		linux-acpi@vger.kernel.org linux-acpi@archiver.kernel.org
	public-inbox-index linux-acpi

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-acpi


AGPL code for this site: git clone https://public-inbox.org/ public-inbox