[PATCH v4 06/13] drm/bridge: lvds-codec: Add "lvds-decoder" support

[Fabrizio Castro]

> From: linux-renesas-soc-owner at vger.kernel.org <linux-renesas-soc-owner at vger.kernel.org> On Behalf Of Laurent Pinchart
> Sent: 17 December 2019 23:09
> Subject: Re: [PATCH v4 06/13] drm/bridge: lvds-codec: Add "lvds-decoder" support
> 
> On Tue, Dec 17, 2019 at 10:06:14PM +0000, Fabrizio Castro wrote:
> > On 17 December 2019 13:54, Laurent Pinchart wrote:
> > > On Tue, Dec 17, 2019 at 01:38:51PM +0100, Geert Uytterhoeven wrote:
> > >> On Tue, Dec 17, 2019 at 1:31 PM Fabrizio Castro wrote:
> > >>> On 17 December 2019 12:21, Geert Uytterhoeven wrote:
> > >>>> On Tue, Dec 17, 2019 at 12:03 PM Fabrizio Castro wrote:
> > >>>>> On 13 December 2019 17:11, Laurent Pinchart wrote:
> > >>>>>> On Wed, Nov 13, 2019 at 03:51:25PM +0000, Fabrizio Castro wrote:
> > >>>>>>> Add support for transparent LVDS decoders by adding a new
> > >>>>>>> compatible string ("lvds-decoder") to the driver.
> > >>>>>>> This patch also adds member connector_type to struct lvds_codec,
> > >>>>>>> and that's because LVDS decoders have a different connector type
> > >>>>>>> from LVDS encoders. We fill this new member up with the data
> > >>>>>>> matching the compatible string.
> > >>>>>>>
> > >>>>>>> Signed-off-by: Fabrizio Castro <fabrizio.castro at bp.renesas.com>
> > >>>>>>>
> > >>>>>>> --- a/drivers/gpu/drm/bridge/lvds-codec.c
> > >>>>>>> +++ b/drivers/gpu/drm/bridge/lvds-codec.c
> > >>>>>>>
> > >>>>>>> @@ -65,6 +67,7 @@ static int lvds_codec_probe(struct platform_device *pdev)
> > >>>>>>>     if (!lvds_codec)
> > >>>>>>>             return -ENOMEM;
> > >>>>>>>
> > >>>>>>> +   lvds_codec->connector_type = (u32)of_device_get_match_data(&pdev->dev);
> > >>>>>>
> > >>>>>> I'm now getting a compilation failure here:
> > >>>>>>
> > >>>>>> drivers/gpu/drm/bridge/lvds-codec.c: In function ‘lvds_codec_probe’:
> > >>>>>> drivers/gpu/drm/bridge/lvds-codec.c:68:31: error: cast from pointer to integer of different size [-Werror=pointer-to-int-
> cast]
> > >>>>>>   lvds_codec->connector_type = (u32)of_device_get_match_data(&pdev->dev);
> > >>>>>>                                ^
> > >>>>>>
> > >>>>>> The fix should be simple:
> > >>>>>>
> > >>>>>>       lvds_codec->connector_type = (uintptr_t)of_device_get_match_data(dev);
> > >>>>>>
> > >>>>>> I'm bothered by the fact that I've compiled this before without any
> > >>>>>> issue, so this really puzzles me. Do you get the same warning ?
> > >>>>>
> > >>>>> The warning appears when compiling for arm64, understandably so.
> > >>>>> We must have compiled this for arm only the first time around.
> > >>>>>
> > >>>>> I think the right way to solve this is to either cast to (u32)(uintptr_t) or (u32)(unsigned long).
> > >>>>
> > >>>> Just casting to uintptr_t should be sufficient.
> > >>>
> > >>> It should be sufficient for the compiler, but I have seen examples where people
> > >>> preferred to be explicit, like in:
> > >>> drivers/mailbox/mtk-cmdq-mailbox.c
> > >>> drivers/leds/leds-pm8058.c
> > >>>
> > >>> Since the kernel is increasing its tightness with respect to warnings, I personally prefer
> > >>> (u32)(uintptr_t), even though not strictly necessary, but I am fine with (uintptr_t) if you
> > >>> don't like (u32)(uintptr_t).
> > >>
> > >> It depends. I try to have as few casts as possible ("casts are evil").
> > >>
> > >> While adding the extra (u32) cast makes it clearer that the intended
> > >> result is a u32 (for now), it will cause silent truncation on 64-bit if
> > >> connector_type is ever enlarged to unsigned long, and larger values are
> > >> used.
> > >>
> > >> In this particular case this is unlikely, though, as unsigned long would
> > >> still be 32-bit on 32-bit platforms, so the larger values cannot be
> > >> used.
> > >
> > > I also try to add as few casts as possible, so (uintptr_t) would be my
> > > preference.
> > >
> > > Fabrizio, could you submit a new version of this patch with the problem
> > > fixed (and with the casts you decide to use, but using uintptr_t instead
> > > of unsigned long in any case) ?
> >
> > Will send a new version tomorrow with (uintptr_t)
> 
> Done as v4.1 :-)

Thank you!

Fab

> 
> --
> Regards,
> 
> Laurent Pinchart