Re: [V7, 2/2] media: i2c: dw9768: Add DW9768 VCM driver

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Dongchun Zhu <dongchun.zhu@mediatek.com>
Cc: mark.rutland@arm.com, devicetree@vger.kernel.org,
	drinkcat@chromium.org, louis.kuo@mediatek.com,
	srv_heupstream@mediatek.com, linus.walleij@linaro.org,
	shengnan.wang@mediatek.com, tfiga@chromium.org,
	bgolaszewski@baylibre.com, sj.huang@mediatek.com,
	robh+dt@kernel.org, linux-mediatek@lists.infradead.org,
	sakari.ailus@linux.intel.com, matthias.bgg@gmail.com,
	bingbu.cao@intel.com, mchehab@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-media@vger.kernel.org
Subject: Re: [V7, 2/2] media: i2c: dw9768: Add DW9768 VCM driver
Date: Tue, 9 Jun 2020 14:14:28 +0300	[thread overview]
Message-ID: <20200609111428.GH2428291@smile.fi.intel.com> (raw)
In-Reply-To: <1591674341.8804.628.camel@mhfsdcap03>

On Tue, Jun 09, 2020 at 11:45:41AM +0800, Dongchun Zhu wrote:
> On Mon, 2020-06-08 at 16:27 +0300, Andy Shevchenko wrote:
> > On Sat, Jun 06, 2020 at 02:19:18PM +0800, Dongchun Zhu wrote:
> > > On Fri, 2020-06-05 at 15:46 +0300, Andy Shevchenko wrote:
> > > > On Fri, Jun 05, 2020 at 06:54:12PM +0800, Dongchun Zhu wrote:

...

> > > > > +#define DW9768_AAC_TIME_DEFAULT			0x20
> > > > 
> > > > Hex? Why not decimal?
> > > > 
> > > 
> > > There is one optional property 'dongwoon,aac-timing' defined in DT.
> > > I don't know whether you have noticed that.
> > > 
> > > 'DW9768_AAC_TIME_DEFAULT' is the value set to AACT[5:0] register.
> > > I thought the Hex unit should be proper as it is directly written to the
> > > Hex register.
> > 
> > I see. I would rather put it like (BIT(6) / 2) to show explicitly that we
> > choose half of the resolution.
> > 
> 
> I knew your idea.
> '(BIT(6) / 2)' may somewhat show the meaning of 'median of the total
> range of AACT[5:0]'.
> 
> But this value is still very obscure relative to '0x20'.
> As I thought that simple is the best, especially for kernel upstream
> patch.

Okay, let's wait for maintainers to speak up.

...

> > > > > +	for ( ; val >= 0; val -= DW9768_MOVE_STEPS) {
> > > > > +		ret = dw9768_set_dac(dw9768, val);
> > > > > +		if (ret) {
> > > > > +			dev_err(&client->dev, "I2C write fail: %d", ret);
> > > > > +			return ret;
> > > > > +		}
> > > > > +		usleep_range(move_delay_us, move_delay_us + 1000);
> > > > > +	}
> > > > 
> > > > 
> > > > It will look more naturally in the multiplier kind of value.
> > > > 
> > > > 	unsigned int steps = DIV_ROUND_UP(...);
> > > > 
> > > > 	while (steps--) {
> > > > 		...(..., steps * ..._MOVE_STEPS);
> > > > 		...
> > > > 	}
> > > > 
> > > > but double check arithmetics.
> > > 
> > > The current coding style is actually updated with reference to your
> > > previous comments on DW9768 v3:
> > > https://patchwork.linuxtv.org/patch/61856/
> > 
> > I understand, but can you consider to go further and see if the proposal works?
> > 
> 
> In fact, your suggestion is something like one another method to set DAC
> value to actuator.
> It is like there may be several solutions to a question.
> 
> Yes. I just tried the new method and it works as expected.
> u32 steps = DIV_ROUND_UP(dw9768->focus->val, DW9768_MOVE_STEPS);
> while (steps--) {
> 	ret = dw9768_set_dac(dw9768, steps * DW9768_MOVE_STEPS);
> 	if (ret)
> 		return ret;
> 	usleep_range(move_delay_us, move_delay_us + 1000);
> }
> 
> But from my perspective, I may prefer to the original method.
> As here what we really care is the DAC value,
> 'dw9768_set_dac(dw9768, val)' seems more simple.

OK.

-- 
With Best Regards,
Andy Shevchenko

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