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Date:   Wed, 24 Nov 2021 13:45:37 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Shubhrajyoti Datta <shubhraj@xilinx.com>
Cc:     "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
        "jirislaby@kernel.org" <jirislaby@kernel.org>,
        "jacmet@sunsite.dk" <jacmet@sunsite.dk>, git <git@xilinx.com>
Subject: Re: [PATCH v2] serial-uartlite: Remove an un-necessary read of
 control register
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On Wed, Nov 24, 2021 at 12:37:00PM +0000, Shubhrajyoti Datta wrote:
> 
> 
> > -----Original Message-----
> > From: Greg KH <gregkh@linuxfoundation.org>
> > Sent: Wednesday, November 24, 2021 3:38 PM
> > To: Shubhrajyoti Datta <shubhraj@xilinx.com>
> > Cc: linux-serial@vger.kernel.org; jirislaby@kernel.org; jacmet@sunsite.dk; git
> > <git@xilinx.com>
> > Subject: Re: [PATCH v2] serial-uartlite: Remove an un-necessary read of control
> > register
> > 
> > On Tue, Nov 23, 2021 at 06:43:48PM +0530, Shubhrajyoti Datta wrote:
> > > The control register is a writeonly register that's why reading it
> > > doesn't make any sense.
> > > The manual states "This is a write-only register. Issuing a read
> > > request to the control register generates the read acknowledgment with zero
> > data."
> > 
> > Are you sure this is ok to remove?  Usually you have to do a read after a write to
> > ensure that the write succeeded.
> > 
> > What ensures that the write succeeded now if you remove this read?
> 
> I do not find the mention of a read requirement in the manual. 

Look at your hardware bus documentation.

> Also in the current code in ulite_console_write and in ulite_startup we are writing without a 
> read. 

So is that a bug there?

I am _very_ loath to remove reads like until you can guarantee that it
will not break anything.  Please work with your hardware designers to
ensure this.

thanks,

greg k-h