Re: [PATCH v6 2/4] leds: Add driver for Qualcomm LPG

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Sun 18 Apr 16:54 CDT 2021, Marijn Suijten wrote:

> Hi Bjorn,
> 
> On 10/21/20 10:12 PM, Bjorn Andersson wrote:
> > The Light Pulse Generator (LPG) is a PWM-block found in a wide range of
> > PMICs from Qualcomm. It can operate on fixed parameters or based on a
> > lookup-table, altering the duty cycle over time - which provides the
> > means for e.g. hardware assisted transitions of LED brightness.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> > Tested-by: Luca Weiss <luca@z3ntu.xyz>
> 
> 
> Thanks for these patches.  I have tested them successfully on the Sony
> Xperia XA2 (Discovery, Nile platform) with the leds on the PM660l - feel
> free to add my Tested-by.  Should I send the configuration your way for
> inclusion in this patch, or submit them separately (either applied after, or
> included as separate patches in the next version of this series)?
> 

Thanks for testing, let's try to land this first iteration first and
then we can add PM660l and PM8150* definitions/support on top.

> > +/**
> > + * struct lpg_data - initialization data
> > + * @lut_base:		base address of LUT block
> > + * @lut_size:		number of entries in LUT
> > + * @triled_base:	base address of TRILED
> > + * @pwm_9bit_mask:	bitmask for switching from 6bit to 9bit pwm
> 
> 
> Our downstream kernel derives this from the "LPG subtype" for each distinct
> channel, read from register offset +0x5.  A value of 0xb is subtype "PWM"
> with a shift of 2, a value of 0x11 is subtype "LPG_LITE" with a shift of 4.
> Can we do the same here instead of hardcoding it for all channels in the LPG
> at once?  How should we determine if the mask is one or two bits wide, for
> the 3<<4 case?
> 

I don't see any obvious solution to the latter, so perhaps we should
just stick with defining this per compatible? Or am I reading your
suggestion wrong?

> > + * @num_channels:	number of channels in LPG
> > + * @channels:		list of channel initialization data
> > + */
> 
> > +	if (ping_pong) {
> > +		if (len % 2)
> > +			hi_pause = 0;
> > +		else
> > +			hi_pause = pattern[len + 1 / 2].delta_t;
> 
> 
> len + 1 should be wrapped in parentheses just like the reassignment to len=
> below, otherwise this is always an out of bounds read (at len + 0).
> 

Thanks for spotting this.

> > +		lo_pause = pattern[len - 1].delta_t;
> > +
> > +		len = (len + 1) / 2;
> > +	} else {
> > +		hi_pause = pattern[len - 1].delta_t;
> > +		lo_pause = 0;
> > +	}
> > +
> > +	ret = lpg_lut_store(lpg, pattern, len, &lo_idx, &hi_idx);
> > +	if (ret < 0)
> > +		goto out;
> > +
> > +	for (i = 0; i < led->num_channels; i++) {
> > +		chan = led->channels[i];
> > +
> > +		chan->ramp_duration_ms = pattern[0].delta_t * len;
> 
> 
> Perhaps this could store the duration of a single step instead, since the
> only use in lpg_apply_lut_control divides it by pattern length again?
> 

Sounds like a good idea.

> > +		chan->ramp_ping_pong = ping_pong;
> > +		chan->ramp_oneshot = repeat != -1;
> > +
> > +		chan->ramp_lo_pause_ms = lo_pause;
> > +		chan->ramp_hi_pause_ms = hi_pause;
> > +
> > +		chan->pattern_lo_idx = lo_idx;
> > +		chan->pattern_hi_idx = hi_idx;
> > +	}
> > +
> > +out:
> > +	return ret;
> > +}
> 
> > +static int lpg_init_lut(struct lpg *lpg)
> > +{
> > +	const struct lpg_data *data = lpg->data;
> > +	size_t bitmap_size;
> > +
> > +	if (!data->lut_base)
> > +		return 0;
> > +
> > +	lpg->lut_base = data->lut_base;
> > +	lpg->lut_size = data->lut_size;
> > +
> > +	bitmap_size = BITS_TO_LONGS(lpg->lut_size) * sizeof(unsigned long);
> > +	lpg->lut_bitmap = devm_kzalloc(lpg->dev, bitmap_size, GFP_KERNEL);
> 
> 
> Would it be nicer to use BITS_TO_BYTES here, or otherwise devm_kcalloc(...,
> bitmap_size, sizeof(long), ...) without mutiplying with sizeof(unsigned
> long)?
> 

Yes, that's cleaner.

> > +
> > +	bitmap_clear(lpg->lut_bitmap, 0, lpg->lut_size);
> > +	return lpg->lut_bitmap ? 0 : -ENOMEM;
> > +}
> > +
> > +static int lpg_probe(struct platform_device *pdev)
> > +{
> > +	struct device_node *np;
> > +	struct lpg *lpg;
> > +	int ret;
> > +	int i;
> > +
> > +	lpg = devm_kzalloc(&pdev->dev, sizeof(*lpg), GFP_KERNEL);
> > +	if (!lpg)
> > +		return -ENOMEM;
> > +
> > +	lpg->data = of_device_get_match_data(&pdev->dev);
> > +	if (!lpg->data)
> > +		return -EINVAL;
> > +
> > +	lpg->dev = &pdev->dev;
> > +
> > +	lpg->map = dev_get_regmap(pdev->dev.parent, NULL);
> > +	if (!lpg->map) {
> > +		dev_err(&pdev->dev, "parent regmap unavailable\n");
> > +		return -ENXIO;
> > +	}
> > +
> > +	ret = lpg_init_channels(lpg);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	ret = lpg_init_triled(lpg);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	ret = lpg_init_lut(lpg);
> > +	if (ret < 0)
> > +		return ret;
> 
> 
> How about turning these returns into dev_err_probe?  I'm not sure if that's
> the expected way to go nowadays, but having some form of logging when a
> driver fails to probe is always good to have.
> 

The intention is that each code path through these functions will either
pass or spit out an error in the log. I looked through them again and
think I cover all paths...

Thanks,
Bjorn