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 15:10:57 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        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 Fri, Nov 12, 2021 at 03:19:17PM +0100, Marijn Suijten wrote:
> On 2021-11-12 13:23:36, Daniel Thompson wrote:
> > On Fri, Nov 12, 2021 at 01:45:22PM +0100, Marijn Suijten wrote:
> > > 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.
> > 
> > Personally I would just squash them together. There are no redundant
> > values in the DT that could be fixed until we can use the string_len
> > to set num_strings.
> 
> Reordering this patch before patch 4 in the way described above should
> allow just that, except that no warnings will be given for ambiguity
> until patch 4 is applied after that - which is weird given that that
> patch only intends the off-by-one error.  Perhaps we should keep the
> order as it is, but add the ambiguity warning in this patch instead.

That works for me. Sounds good.


Daniel.