linux-kernel - Re: [alsa-devel] [PATCH v2 3/3] ASoC: TDA7802: Add turn-on diagnostic routine

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Message-ID: <45156592-a90f-b4f8-4d30-9631c03f1280@codethink.co.uk>
Date:   Tue, 30 Jul 2019 16:25:56 +0100
From:   Thomas Preston <thomas.preston@...ethink.co.uk>
To:     Mark Brown <broonie@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org,
        alsa-devel@...a-project.org,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Kirill Marinushkin <kmarinushkin@...dec.tech>,
        Cheng-Yi Chiang <cychiang@...omium.org>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Takashi Iwai <tiwai@...e.com>,
        Annaliese McDermond <nh6z@...z.net>,
        Liam Girdwood <lgirdwood@...il.com>,
        Paul Cercueil <paul@...pouillou.net>,
        Vinod Koul <vkoul@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        linux-kernel@...r.kernel.org, Jerome Brunet <jbrunet@...libre.com>
Subject: Re: [alsa-devel] [PATCH v2 3/3] ASoC: TDA7802: Add turn-on diagnostic
 routine

On 30/07/2019 15:19, Mark Brown wrote:
> On Tue, Jul 30, 2019 at 01:09:37PM +0100, Thomas Preston wrote:
> 
>> +	struct dentry *debugfs;
>> +	struct mutex diagnostic_mutex;
>> +};
> 
> It is unclear what this mutex usefully protects, it only gets taken when
> writing to the debugfs file to trigger this diagnostic mode but doesn't
> do anything to control interactions with any other code path in the
> driver.
> 

If another process reads the debugfs node "diagnostic" while the turn-on 
diagnostic mode is running, this mutex prevents the second process
restarting the diagnostics.

This is redundant if debugfs reads are atomic, but I don't think they are.


>> +static int run_turn_on_diagnostic(struct tda7802_priv *tda7802, u8 *status)
>> +{
>> +	struct device *dev = &tda7802->i2c->dev;
>> +	int err_status, err;
>> +	unsigned int val;
>> +	u8 state[NUM_IB];
> 
>> +	/* We must wait 20ms for device to settle, otherwise diagnostics will
>> +	 * not start and regmap poll will timeout.
>> +	 */
>> +	msleep(DIAGNOSTIC_SETTLE_MS);
> 
> The comment and define might go out of sync...
> 

Thanks, I will remove the 20ms but keep the comment here.

>> +	err = regmap_bulk_read(tda7802->regmap, TDA7802_DB1, status, 4);
>> +	if (err < 0) {
>> +		dev_err(dev, "Could not read channel status, %d\n", err);
>> +		goto diagnostic_restore;
>> +	}
> 
> ...but here we use a magic number for the array size :(
> 

Thanks, will update.

>> +static int tda7802_diagnostic_show(struct seq_file *f, void *p)
>> +{
>> +	char *buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
> 
> We neither use nor free buf?
> 
>> +static int tda7802_probe(struct snd_soc_component *component)
>> +{
>> +	struct tda7802_priv *tda7802 = snd_soc_component_get_drvdata(component);
>> +	struct device *dev = &tda7802->i2c->dev;
>> +	int err;
> 
> Why is this done at the component level?
> 

Argh my bad, a previous iteration required the buf and component. I missed
this, sorry for the noise.

Thanks for feedback, I'll go back and tend to all of this.