linux-kernel - Re: [PATCH v3 3/4] leds: pca955x: Optimize probe led selection

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Date:   Wed, 4 May 2022 19:24:29 +0200
From:   Pavel Machek <pavel@....cz>
To:     Eddie James <eajames@...ux.ibm.com>
Cc:     linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
        patrick@...cx.xyz, andy.shevchenko@...il.com,
        openbmc@...ts.ozlabs.org, joel@....id.au
Subject: Re: [PATCH v3 3/4] leds: pca955x: Optimize probe led selection

Hi!

> Previously, the probe function might do up to 32 reads and writes
> to the same 4 registers to program the led selection. Reduce this to
> a maximum of 8 operations by accumulating the changes to the led
> selection and comparing with the previous value to write the
> selection if different.

We have regmap APIs. You are free to use them if you really care about
those few reads. Reimplementing them by hand is not acceptable. How big is 
the seedup here?

Best regards,
								Pavel

> @@ -554,6 +556,15 @@ static int pca955x_probe(struct i2c_client *client)
>  	init_data.devname_mandatory = false;
>  	init_data.devicename = "pca955x";
>  
> +	nls = pca955x_num_led_regs(chip->bits);
> +	for (i = 0; i < nls; ++i) {
> +		err = pca955x_read_ls(pca955x, i, &ls1[i]);
> +		if (err)
> +			return err;
> +
> +		ls2[i] = ls1[i];
> +	}
> +
>  	for (i = 0; i < chip->bits; i++) {
>  		pca955x_led = &pca955x->leds[i];
>  		pca955x_led->led_num = i;
> @@ -624,6 +634,14 @@ static int pca955x_probe(struct i2c_client *client)
>  		}
>  	}
>  
> +	for (i = 0; i < nls; ++i) {
> +		if (ls1[i] != ls2[i]) {
> +			err = pca955x_write_ls(pca955x, i, ls2[i]);
> +			if (err)
> +				return err;
> +		}
> +	}
> +
>  	/* PWM0 is used for half brightness or 50% duty cycle */
>  	err = pca955x_write_pwm(pca955x, 0, 255 - LED_HALF);
>  	if (err)

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html