linux-kernel - Re: [RESEND PATCH v2 05/13] backlight: qcom-wled: Override default length with qcom,enabled-strings

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Date:   Fri, 12 Nov 2021 13:45:22 +0100
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     phone-devel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Pavel Dubrova <pashadubrova@...il.com>,
        Kiran Gunda <kgunda@...eaurora.org>,
        Bryan Wu <cooloney@...il.com>, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org
Subject: Re: [RESEND PATCH v2 05/13] backlight: qcom-wled: Override default
 length with qcom,enabled-strings

On 2021-11-12 12:12:38, Daniel Thompson wrote:
> On Fri, Nov 12, 2021 at 01:26:58AM +0100, Marijn Suijten wrote:
> > The length of qcom,enabled-strings as property array is enough to
> > determine the number of strings to be enabled, without needing to set
> > qcom,num-strings to override the default number of strings when less
> > than the default (which is also the maxium) is provided in DT.
> > 
> > Fixes: 775d2ffb4af6 ("backlight: qcom-wled: Restructure the driver for WLED3")
> > Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> > Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>
> > ---
> >  drivers/video/backlight/qcom-wled.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/video/backlight/qcom-wled.c b/drivers/video/backlight/qcom-wled.c
> > index c5232478a343..9bfbf601762a 100644
> > --- a/drivers/video/backlight/qcom-wled.c
> > +++ b/drivers/video/backlight/qcom-wled.c
> > @@ -1518,6 +1518,8 @@ static int wled_configure(struct wled *wled)
> >  				return -EINVAL;
> >  			}
> >  		}
> > +
> > +		cfg->num_strings = string_len;
> 
> I still don't really understand why this wants to be a separate patch.

I'm viewing this as a separate issue, and this makes it easier to
document the change in a loose commit.

> The warning text emitted by the previous patch (whatever text we agree
> on) will be nonsense until this patch is applied.
> 
> If this patch cannot appear before the warning is introduces then there
> is no correct order for patches 4 and 5 (which implies they should be the
> same patch).

Agreed, this is a weird way of doing things in v2 - the error message is
printed yet the length of qcom,enabled-strings is always ignored before
this patch.

If we were to reorder patch 5 before patch 4 that should also
temporarily move `cfg->num_strings = cfg->num_strings + 1;` right below
this `if` so that `qcom,num-strings` remains the definitive way to
set/override length.  That's doable, and makes it easier to read patch 4
as that bit of code will be replaced by of_property_read_u32 on that
exact line.  Let me know which method you prefer.

- Marijn