linux-kernel - RE: [PATCH v3 char-misc-next] misc: microchip: pci1xxxx: Add OTP/EEPROM driver for the pci1xxxx switch

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Message-ID: <PH7PR11MB59589EE1C7787496316C04339BDA9@PH7PR11MB5958.namprd11.prod.outlook.com>
Date:   Mon, 6 Feb 2023 17:03:57 +0000
From:   <Tharunkumar.Pasumarthi@...rochip.com>
To:     <gregkh@...uxfoundation.org>
CC:     <Kumaravel.Thiagarajan@...rochip.com>, <arnd@...db.de>,
        <linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>,
        <UNGLinuxDriver@...rochip.com>, <lkp@...el.com>
Subject: RE: [PATCH v3 char-misc-next] misc: microchip: pci1xxxx: Add
 OTP/EEPROM driver for the pci1xxxx switch

> From: Greg KH <gregkh@...uxfoundation.org>
> Sent: Monday, February 6, 2023 3:12 PM
> To: Tharunkumar Pasumarthi - I67821
> <Tharunkumar.Pasumarthi@...rochip.com>
> > > > +     delay = msecs_to_jiffies(OTP_RW_TIMEOUT_MILLISECONDS);
> > > > +     j0 = jiffies;
> > > > +     j1 = j0 + delay;
> > >
> > > Are you sure this math works out?  Please use the jiffies math
> > > functions instead so you can handle wrapping properly.
> >
> > You suggest using any existing APIs to add jiffies to handle wrapping?
> > I am not able to find any such API. Can you please point out API name.
> 
> I have no context here for what you are doing with the math in jiffies, but
> that is usually a very odd thing.  If you use the normal timer functions, you
> will not have to worry about the wrapping as it is handled for you, right?

Hi Greg,
Our objective with that part of code is to wait for OTP_STATUS_BUSY_BIT 
to be cleared in the hardware, but make sure that we wait for a maximum 
of OTP_RW_TIMEOUT_MILLISECONDS ms in the driver and not beyond that. 
This logic is not possible with normal timer functions. Timer wrapping logic is 
handled by time_before API internally. So, there does not seem to be issue with
existing code. 

Thanks,
Tharun Kumar P