Re: [PATCH v2] serial-uartlite: Remove an un-necessary read of control register

On Wed, Nov 24, 2021 at 12:37:00PM +0000, Shubhrajyoti Datta wrote:

quoted

-----Original Message-----
From: Greg KH <gregkh@linuxfoundation.org>
Sent: Wednesday, November 24, 2021 3:38 PM
To: Shubhrajyoti Datta <redacted>
Cc: linux-serial@vger.kernel.org; jirislaby@kernel.org; jacmet@sunsite.dk; git
[off-list ref]
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:

quoted

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