Message-ID: <505C96E9.3080307@convergeddevices.net>
Date:	Fri, 21 Sep 2012 09:33:45 -0700
From:	"andrey.smirnov@...vergeddevices.net" 
	<andrey.smirnov@...vergeddevices.net>
To:	Hans Verkuil <hverkuil@...all.nl>
CC:	<linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] Add a core driver for SI476x MFD

On 09/21/2012 12:31 AM, Hans Verkuil wrote:
> On Fri September 21 2012 03:05:41 andrey.smirnov@...vergeddevices.net wrote:
>> On 09/13/2012 11:44 PM, Hans Verkuil wrote:
>>> Hi Andrey!
>>>
>>> Thanks for posting this driver. One request for the future: please split this
>>> patch up in smaller pieces: one for each c source for example. That makes it
>>> easier to review.
>> Will do for next version.
>>
>>> +
>>> +/**
>>> + * __core_send_command() - sends a command to si476x and waits its
>>> + * response
>>> + * @core:    si476x_device structure for the device we are
>>> + *            communicating with
>>> + * @command:  command id
>>> + * @args:     command arguments we are sending
>>> + * @argn:     actual size of @args
>>> + * @response: buffer to place the expected response from the device
>>> + * @respn:    actual size of @response
>>> + * @usecs:    amount of time to wait before reading the response (in
>>> + *            usecs)
>>> + *
>>> + * Function returns 0 on succsess and negative error code on
>>> + * failure
>>> + */
>>> +static int __core_send_command(struct si476x_core *core,
>>> +				    const u8 command,
>>> +				    const u8 args[],
>>> +				    const int argn,
>>> +				    u8 resp[],
>>> +				    const int respn,
>>> +				    const int usecs)
>>> +{
>>> +	struct i2c_client *client = core->client;
>>> +	int err;
>>> +	u8  data[CMD_MAX_ARGS_COUNT + 1];
>>> +
>>> +	if (argn > CMD_MAX_ARGS_COUNT) {
>>> +		err = -ENOMEM;
>>> +		goto exit;
>>> Why goto exit? There is no clean up after the exit label, so just return
>>> immediately. Ditto for all the other goto exit's in this function.
>> To have only just on point of exit from the function that's just
>> personal coding style preference.
>> There are no technical reasons behind that, I can change that.
>>
>>>> +	}
>>>> +
>>>> +	if (!client->adapter) {
>>>> +		err = -ENODEV;
>>>> +		goto exit;
>>>> +	}
>>>> +
>>>> +	/* First send the command and its arguments */
>>>> +	data[0] = command;
>>>> +	memcpy(&data[1], args, argn);
>>>> +	DBG_BUFFER(&client->dev, "Command:\n", data, argn + 1);
>>>> +
>>>> +	err = si476x_i2c_xfer(core, SI476X_I2C_SEND, (char *) data, argn + 1);
>>>> +	if (err != argn + 1) {
>>>> +		dev_err(&core->client->dev,
>>>> +			"Error while sending command 0x%02x\n",
>>>> +			command);
>>>> +		err = (err >= 0) ? -EIO : err;
>>>> +		goto exit;
>>>> +	}
>>>> +	/* Set CTS to zero only after the command is send to avoid
>>>> +	 * possible racing conditions when working in polling mode */
>>>> +	atomic_set(&core->cts, 0);
>>>> +
>>>> +	if (!wait_event_timeout(core->command,
>>>> +				atomic_read(&core->cts),
>>>> +				usecs_to_jiffies(usecs) + 1))
>>>> +		dev_warn(&core->client->dev,
>>>> +			 "(%s) [CMD 0x%02x] Device took too much time to answer.\n",
>>>> +			 __func__, command);
>>>> +
>>>> +	/*
>>>> +	  When working in polling mode, for some reason the tuner will
>>>> +	  report CTS bit as being set in the first status byte read,
>>>> +	  but all the consequtive ones will return zros until the
>>>> +	  tuner is actually completed the POWER_UP command. To
>>>> +	  workaround that we wait for second CTS to be reported
>>>> +	 */
>>>> +	if (unlikely(!core->client->irq && command == CMD_POWER_UP)) {
>>>> +		if (!wait_event_timeout(core->command,
>>>> +					atomic_read(&core->cts),
>>>> +					usecs_to_jiffies(usecs) + 1))
>>>> +			dev_warn(&core->client->dev,
>>>> +				 "(%s) Power up took too much time.\n",
>>>> +				 __func__);
>>>> +	}
>>>> +
>>>> +	/* Then get the response */
>>>> +	err = si476x_i2c_xfer(core, SI476X_I2C_RECV, resp, respn);
>>>> +	if (err != respn) {
>>>> +		dev_err(&core->client->dev,
>>>> +			"Error while reading response for command 0x%02x\n",
>>>> +			command);
>>>> +		err = (err >= 0) ? -EIO : err;
>>>> +		goto exit;
>>>> +	}
>>>> +	DBG_BUFFER(&client->dev, "Response:\n", resp, respn);
>>>> +
>>>> +	err = 0;
>>>> +
>>>> +	if (resp[0] & SI476X_ERR) {
>>>> +		dev_err(&core->client->dev, "Chip set error flag\n");
>>>> +		err = si476x_core_parse_and_nag_about_error(core);
>>>> +		goto exit;
>>>> +	}
>>>> +
>>>> +	if (!(resp[0] & SI476X_CTS))
>>>> +		err = -EBUSY;
>>>> +exit:
>>>> +	return err;
>>>> +}
>>>> +
>>>> +#define CORE_SEND_COMMAND(core, cmd, args, resp, timeout)		\
>>>> +	__core_send_command(core, cmd, args,				\
>>>> +			    ARRAY_SIZE(args),				\
>>>> +			    resp, ARRAY_SIZE(resp),			\
>>>> +			    timeout)
>>>> +
>>>> +
>>>> +static int __cmd_tune_seek_freq(struct si476x_core *core,
>>>> +				uint8_t cmd,
>>>> +				const uint8_t args[], size_t argn,
>>>> +				uint8_t *resp, size_t respn,
>>>> +				int (*clear_stcint) (struct si476x_core *core))
>>>> +{
>>>> +	int err;
>>>> +
>>>> +	atomic_set(&core->stc, 0);
>>>> +	err = __core_send_command(core, cmd, args, argn,
>>>> +				  resp, respn,
>>>> +				  atomic_read(&core->timeouts.command));
>>>> +	if (!err) {
>>> Invert the test to simplify indentation.
>>>
>>>> +		if (!wait_event_timeout(core->tuning,
>>>> +		atomic_read(&core->stc),
>>>> +		usecs_to_jiffies(atomic_read(&core->timeouts.tune)) + 1)) {
>>> Weird indentation above. Indent the arguments more to the right.
>> 80 symbol line length limit is the reason for that indentation.
> It's not a limit, it's a warning only. Usually readability improves if such
> long lines are split up or otherwise shortened, but if readability becomes
> worse because of that, then just leave in the long line.
>
>>> Andrey, you should look at the drivers/media/radio/si4713-i2c.c source.
>>> It is for the same chip family and is much, much smaller.
>>>
>>> See if you can use some of the code that's there.
>> I did when I started writing the driver, that driver and driver for
>> wl1273 were my two examples. In my initial version of the driver I tried
>> to blend both si4713 and si476x into one generic driver, but the problem
>> is: si4713 is a transmitter and si476x are receiver chips, the
>> "impedance mismatch" in functionality of the two, IMHO, was too much to
>> justify the unification.
> But the way the commands are handled, etc. should be the same or very similar.
> That's the main area where I suspect you can reuse code from those other
> drivers.

To reuse the si4713_send_command function from si4713 driver I would
have to modify the way IRQs are handled by that driver and basically
replace its code for mine. And the reason for that is because si4761 is
a receiver, I cannot just rely on timeouts in the case of driver working
in "no-IRQ" mode(current implementation in si4713 driver). I need a
polling loop that would allow me to receive RDS and monitor the status
of the chip. Plus having a polling loop allows me to have almost
identical implementation of chip events handling for both cases(IRQ and
no-IRQ). I don't feel comfortable making such drastic changes to si4713
driver without having access to the actual hardware and being ability to
test it.

I really did try to amalgamate two drivers into a single one(and even
received an earful from my, at that time, supervisor for wasting my time
on it). But as I mentioned earlier to unite both drivers I would have to
modify si4713's code and without any actual hardware I cannot do it.

Andrey

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