linux-kernel - Re: [PATCH v3 5/5] meson saradc: support reading from channel 7 mux inputs

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Message-ID: <93dbcbb6-ee17-270c-328d-677e1e3338b3@sberdevices.ru>
Date:   Tue, 4 Jul 2023 11:08:36 +0300
From:   George Stark <gnstark@...rdevices.ru>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
CC:     <jic23@...nel.org>, <lars@...afoo.de>, <neil.armstrong@...aro.org>,
        <khilman@...libre.com>, <jbrunet@...libre.com>,
        <andriy.shevchenko@...ux.intel.com>, <nuno.sa@...log.com>,
        <linux-iio@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-amlogic@...ts.infradead.org>, <kernel@...rdevices.ru>
Subject: Re: [PATCH v3 5/5] meson saradc: support reading from channel 7 mux
 inputs

Hello Martin, Jonathan

On 7/3/23 22:39, Martin Blumenstingl wrote:
> Hi Jonathan,
> 
> On Sun, Jul 2, 2023 at 11:21 AM Jonathan Cameron
> <Jonathan.Cameron@...wei.com> wrote:
> [...]
>>> @@ -235,6 +249,27 @@ enum meson_sar_adc_channel_index {
>>>        NUM_CHAN_7,
>>>        NUM_CHAN_TEMP,
>>>        NUM_CHAN_SOFT_TIMESTAMP,
>>
>> Silly question... Why does this device have timestamp channels?
>> It has no buffer support so they don't 'do anything'.
>> If it had then putting other channels after that might have broken
>> things if not done very carefully (hence I went looking)
> This question is probably for me (not George).
> The answer is simple: when I wrote the Meson SAR ADC driver I looked
> at various other drivers (but can't recall which ones exactly). One of
> them probably used a soft timestamp channel so I also added that to
> meson_saradc. Since "it didn't break anything" I thought it would be
> fine.
> 
> Newer SAR ADC IP blocks have buffer support, but that's not
> implemented in the driver (yet).
> So if I understand you correctly we can drop the soft timestamp
> channel (with a dedicated patch in this series)?

One short comment: newly-added channels probably won't support buffering 
because physically they all are read thru channel7. We'll be able to add 
buffering only to base old channels and they are still defined before
CHAN_SOFT_TIMESTAMP in channel array (if this is you're wary about).

> 
> 
> Best regards,
> Martin

-- 
Best regards
George