Re: [PATCH] staging: sm750fb: do not program the PLL from an uninitialized value

[Yuhao Jiang]

On Mon, Aug 17, 2026 at 6:13 AM Dan Carpenter <error27@xxxxxxxxx> wrote:
>
> On Mon, Aug 17, 2026 at 05:49:33AM -0500, Yuhao Jiang wrote:
> > On Mon, Aug 17, 2026 at 4:59 AM Dan Carpenter <error27@xxxxxxxxx> wrote:
> > >
> > > On Mon, Aug 17, 2026 at 05:13:53PM +0800, Junrui Luo via B4 Relay wrote:
> > > > From: Junrui Luo <moonafterrain@xxxxxxxxxxx>
> > > >
> > > > sm750_calc_pll_value() writes pll->M, N, OD and POD only when its search
> > > > loop finds a divider combination with 0 < M < 256, and returns 0 when
> > > > there is none. ddk750_set_mode_timing() discards that return value and
> > > > calls program_mode_registers() regardless, so sm750_format_pll_reg()
> > > > reads the four members uninitialized and pokes them into PANEL_PLL_CTRL
> > > > or CRT_PLL_CTRL. Nothing bounds var->pixclock on the way in, so a mode
> > > > set can ask for a clock the loop cannot represent.
> > > >
> > > > Consume the return value and reject the mode; hw_sm750_crtc_set_mode()
> > > > already propagates a non-zero return. Initialize the structure as well:
> > > > sm750_calc_pll_value() returns early for SM750LE without writing the
> > > > members, and returns non-zero on that path.
> > > >
> > > > Fixes: 81dee67e215b ("staging: sm750fb: add sm750 to staging")
> > > > Reported-by: Yuhao Jiang <danisjiang@xxxxxxxxx>
> > > > Assisted-by: Claude:claude-opus-5
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > > > Signed-off-by: Junrui Luo <moonafterrain@xxxxxxxxxxx>
> > > > ---
> > >
> > > Greg is not taking AI patches unless they can be tested.
> > > https://lore.kernel.org/all/2026080354-skater-urgent-31b2@gregkh/
> > >
> > > I kind of hate AI commit messages...  They are so verbose, confident
> > > and reasonable sounding.  But they don't answer any of the real
> > > questions I want to know.  How did Yuhao Jiang find this bug?  What
> >
> > We're working on an LLM-assisted system for vulnerability discovery,
> > and this bug was found by the system and checked by me.
> >
>
> I feel like this is always part of the story and should be told.
> Regardless the firm rule is that everyone agrees on if you can't test it,
> then that needs to be in the notes under the --- cut off.
>
> (I sometimes skip this, but I've been doing this for a long long time
> and everyone knows who I am.  I should follow the rules too.  #shame).
>
> regards,
> dan carpenter
>

Got it. We will follow this rule in the future. Thanks for the guidance.

-- 
Yuhao Jiang