RE: [EXT] Re: [PATCH v3] i2c: imx-lpi2c: add error message when i2c peripheral clk doesn't work

[Carlos Song]

Hi

> -----Original Message-----
> From: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> Sent: Tuesday, July 25, 2023 2:45 PM
> To: Carlos Song <carlos.song@xxxxxxx>
> Cc: festevam@xxxxxxxxx; andi.shyti@xxxxxxxxxx; Aisheng Dong
> <aisheng.dong@xxxxxxx>; shawnguo@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx;
> kernel@xxxxxxxxxxxxxx; Bough Chen <haibo.chen@xxxxxxx>;
> linux-kernel@xxxxxxxxxxxxxxx; Clark Wang <xiaoning.wang@xxxxxxx>;
> linux-i2c@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; dl-linux-imx
> <linux-imx@xxxxxxx>
> Subject: [EXT] Re: [PATCH v3] i2c: imx-lpi2c: add error message when i2c
> peripheral clk doesn't work
> 
> On Tue, Jul 25, 2023 at 10:11:08AM +0800, carlos.song@xxxxxxx wrote:
> > From: Gao Pan <pandy.gao@xxxxxxx>
> >
> > Output error log when i2c peripheral clk rate is 0, then directly
> > return -EINVAL.
> >
> > Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
> > Signed-off-by: Gao Pan <pandy.gao@xxxxxxx>
> > Signed-off-by: Carlos Song <carlos.song@xxxxxxx>
> > ---
> > Changes for V2:
> > - adjust the Subject from "debug message" to "error message"
> > ---
> >  drivers/i2c/busses/i2c-imx-lpi2c.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c
> > b/drivers/i2c/busses/i2c-imx-lpi2c.c
> > index e93ff3b5373c..12b4f2a89343 100644
> 
> I wonder which tree you based this on. The object e93ff3b5373c is neither in
> v6.5-rc1 nor next nor in Wolfram's tree. (Probably not critical for this patch. But
> if you base your patch on a public tree, you're making things easier for the build
> bots. Related to that I recommend git format-patch --base=...)
> 

I make the patch on linux-next master branch at:
commit 4d2c646ac07cf4a35ef1c4a935a1a4fd6c6b1a36 (tag: next-20230724, origin/master, origin/HEAD)
Author: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Date:   Mon Jul 24 14:07:27 2023 +1000

Just now I git fetch and rebase on the linux-next, now I am on master branch at:
commit 1e25dd7772483f477f79986d956028e9f47f990a (tag: next-20230725, origin/master, origin/HEAD)
Author: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
Date:   Tue Jul 25 14:08:59 2023 +1000

    Add linux-next specific files for 20230725

    Signed-off-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>
I can still git am the patch.

> > --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> > +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> > @@ -214,6 +214,11 @@ static int lpi2c_imx_config(struct lpi2c_imx_struct
> *lpi2c_imx)
> >  	lpi2c_imx_set_mode(lpi2c_imx);
> >
> >  	clk_rate = clk_get_rate(lpi2c_imx->clks[0].clk);
> > +	if (!clk_rate) {
> > +		dev_err(&lpi2c_imx->adapter.dev, "clk_per rate is 0\n");
> > +		return -EINVAL;
> > +	}
> 
> I'm not sure this is a good idea. In my book error messages in functions that
> might be called often (and triggered by user space) do more harm than good as
> they flood the kernel log buffer and so might make it hard to find the original
> cause of the problem. I'd say returning an error code should be enough here.
> 
> Having said that I wonder if you're fixing a real issue? (i.e. did it happen to you
> that clk_rate was 0? Did this result in a div-by-zero? Or a hardware hang? Or a
> too fast (or too slow) bus speed?) Or is this just addressing a warning by some
> static checker?
> 

Thanks for you suggestion. I will rm the line " dev_err(&lpi2c_imx->adapter.dev, "clk_per rate is 0\n");"
And resend the patch.

The per_clk is a critical i2c function clk. If it is 0, it will cause lpi2c can't work. This is a double check for lpi2c clk before configing clk register. It can improve the stability of the driver, even though it rarely triggers.
> Best regards
> Uwe
> 
> --
> Pengutronix e.K.                           | Uwe Kleine-König
> |
> Industrial Linux Solutions                 | https://www.pengutronix.de/ |