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From:   Yusuf Khan <yusisamerican@gmail.com>
Date:   Sat, 26 Feb 2022 02:48:25 -0800
Message-ID: <CAJoG2+_qbu1Ca51exoq+0MSdcGda4y5YxM9vdseDqiH1n_i88A@mail.gmail.com>
Subject: Re: [PATCH] drivers: ddcci: upstream DDCCI driver
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Jason Wang <jasowang@redhat.com>,
        Michael Kelley <mikelley@microsoft.com>,
        "Michael S. Tsirkin" <mst@redhat.com>,
        gregkh <gregkh@linuxfoundation.org>, javier@javigon.com,
        Will Deacon <will@kernel.org>, Jens Axboe <axboe@kernel.dk>,
        Bjorn Andersson <bjorn.andersson@linaro.org>
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Precedence: bulk

Arnd, the driver includes a backlight driver, the main part of the
driver(ddcci.c) is a monitor communication protocol. Should
I leave the backlight driver(ddcci-backlight.c) in drivers/video/backlight?

On Sat, Feb 26, 2022 at 1:39 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> with the other ones.On Sat, Feb 26, 2022 at 3:20 AM Yusuf Khan
> <yusisamerican@gmail.com> wrote:
> >
> > This patch upstreams the DDCCI driver by Christoph Grenz into
> > the kernel. The original gitlab page is loacted at https://gitlab
> > .com/ddcci-driver-linux/ddcci-driver-linux/-/tree/master.
> >
> > Signed-off-by: Yusuf Khan <yusisamerican@gmail.com>
> > ---
> >  drivers/Kconfig                 |    2 +
> >  drivers/Makefile                |    1 +
> >  drivers/ddcci/Kconfig           |    3 +
> >  drivers/ddcci/Makefile          |    3 +
> >  drivers/ddcci/ddcci-backlight.c |  413 +++++++
> >  drivers/ddcci/ddcci.c           | 1895 +++++++++++++++++++++++++++++++
> >  include/linux/ddcci.h           |  164 +++
>
> If this is a backlight driver, I think it should go into
> drivers/video/backlight/,
> no need for a top-level subsystem.
>
> > + */
> > +
> > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> > +#include <asm-generic/fcntl.h>
>
> Including the asm-generic version causes the build failures. If you need
> the contents, use <linux/fcntl.h>, otherwise leave it out.
>
> > +static dev_t ddcci_cdev_first;
> > +static dev_t ddcci_cdev_next;
> > +static dev_t ddcci_cdev_end;
> > +static DEFINE_SEMAPHORE(core_lock);
>
> No new semaphores please, this should probably be a mutex.
>
>
> > +struct bus_type ddcci_bus_type;
> > +EXPORT_SYMBOL_GPL(ddcci_bus_type);
> > +
> > +/* Assert neccessary string array sizes  */
> > +#ifndef sizeof_field
> > +# define sizeof_field(t,m) FIELD_SIZEOF(t,m)
> > +#endif
> > +static_assert(sizeof_field(struct ddcci_device, prot) > 8);
> > +static_assert(sizeof_field(struct ddcci_device, type) > 8);
> > +static_assert(sizeof_field(struct ddcci_device, model) > 8);
> > +static_assert(sizeof_field(struct ddcci_device, vendor) > 8);
> > +static_assert(sizeof_field(struct ddcci_device, module) > 8);
> > +
> > +/* Internal per-i2c-client driver data */
> > +struct ddcci_bus_drv_data {
> > +       unsigned long quirks;
> > +       struct i2c_client *i2c_dev;
> > +       struct semaphore sem;
> > +       unsigned char recv_buffer[DDCCI_RECV_BUFFER_SIZE];
> > +};
>
> Same here.
>
> > +static const struct file_operations ddcci_fops = {
> > +       .owner = THIS_MODULE,
> > +       .read = ddcci_cdev_read,
> > +       .write = ddcci_cdev_write,
> > +       .open = ddcci_cdev_open,
> > +       .release = ddcci_cdev_close,
> > +       .llseek = ddcci_cdev_seek
> > +};
>
> It looks like this adds low-level access to a bus that is already managed by
> the drm (or older framebuffer) drivers. How do you prevent these two
> from stepping on each other's toes?
>
>         Arnd