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Thu, 3 May 2018 10:31:46 -0400 Received: from muru.com ([72.249.23.125]:39946 "EHLO muru.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751088AbeECObp (ORCPT ); Thu, 3 May 2018 10:31:45 -0400 Date: Thu, 3 May 2018 07:31:41 -0700 From: Tony Lindgren To: Vignesh R Cc: Peter Hurley , Greg Kroah-Hartman , Peter Ujfalusi , Sebastian Andrzej Siewior , linux-serial@vger.kernel.org, linux-omap@vger.kernel.org, linux-kernel@vger.kernel.org, Keerthy , Matthijs van Duin , Sekhar Nori , Tero Kristo Subject: Re: [PATCH] serial: 8250: omap: Fix idling of clocks for unused uarts Message-ID: <20180503143141.GR98604@atomide.com> References: <20180502171500.60462-1-tony@atomide.com> <58bcba76-d63b-212e-4baf-d40a28c549d3@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <58bcba76-d63b-212e-4baf-d40a28c549d3@ti.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-serial-owner@vger.kernel.org X-Mailing-List: linux-serial@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: * Vignesh R [180503 10:20]: > > > On Wednesday 02 May 2018 10:45 PM, Tony Lindgren wrote: > > I noticed that unused UARTs won't necessarily idle properly always > > unless at least one byte tx transfer is done first. > > > > After some debugging I narrowed down the problem to the scr register > > dma configuration bits that need to be set before softreset for the > > clocks to idle. Unless we do this, the module clkctrl idlest bits > > may be set to 1 instead of 3 meaning the clock will never idle and > > is blocking deeper idle states for the whole domain. > > > > This might be related to the configuration done by the bootloader > > or kexec booting where certain configurations cause the 8250 or > > the clkctrl clock to jam in a way where setting of the scr bits > > and reset is needed to clear it. I've tried diffing the 8250 > > registers for the various modes, but did not see anything specific. > > So far I've only seen this on omap4 but I'm suspecting this might > > also happen on the other clkctrl using SoCs considering they > > already have a quirk enabled for UART_ERRATA_CLOCK_DISABLE. > > > > That's interesting! We do have AM437x suspend/resume working without > this workaround (UARTs on AM437x does not use DMA) and UART IPs clkctrl > do go to idle state. Seems like a OMAP4 specific issue. Yeah seems to be omap4 specific. I did not see this yesterday on my am437x-idk or beagle-x15 after clearing status = "disabled" for all ports and idling them. > Comment in omap8250_update_scr() warns not to set these two bits in a > single register write because this may lead to malfunction. I would > recommend to split this into two writes. OK I'll split the write into two parts. Regards, Tony