linux-kernel - RE: [PATCH v4] hwmon: (pmbus/max31785) Add delay between bus accesses

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Message-ID: <E8022352-9856-4910-AB38-134BBF4C4E53@us.ibm.com>
Date:   Fri, 27 Oct 2023 03:25:14 +0000
From:   Lakshmi Yadlapati <lakshmiy@...ibm.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "eajames@...ux.ibm.com" <eajames@...ux.ibm.com>,
        "ninad@...ux.ibm.com" <ninad@...ux.ibm.com>,
        "jdelvare@...e.com" <jdelvare@...e.com>
CC:     "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4] hwmon: (pmbus/max31785) Add delay between bus accesses



On 10/26/23, 6:02 PM, "Guenter Roeck" <groeck7@...il.com <mailto:groeck7@...il.com> on behalf of linux@...ck-us.net <mailto:linux@...ck-us.net>> wrote:


On 10/26/23 15:17, Lakshmi Yadlapati wrote:
> The MAX31785 has shown erratic behaviour across multiple system
> designs, unexpectedly clock stretching and NAKing transactions.
> 
> Experimentation shows that this seems to be triggered by a register access
> directly back to back with a previous register write. Experimentation also
> shows that inserting a small delay after register writes makes the issue go
> away.
> 
> Use a similar solution to what the max15301 driver does to solve the same
> problem. Create a custom set of bus read and write functions that make sure
> that the delay is added.
> 
> Signed-off-by: Lakshmi Yadlapati <lakshmiy@...ibm.com <mailto:lakshmiy@...ibm.com>>
> ---
> V3 -> V4: Fixed warnings realted to this commit


>I also asked about the use of udelay() instead of usleep_range() or fsleep().
>I see you did not change the code. Fine, but please explain why the use of
>udelay() instead of the alternative is desirable or needed here, and don't
>just ignore review feedback.

Sorry, I missed the comment, I will make changes and send it again.

Thanks,
Lakshmi

>Thanks,
>Guenter