On Thu, Feb 16, 2012 at 04:57:59PM -0800, Darren Hart wrote: > I'm working on a tunnel creek (atom e6xx + topcliff PCH) development platform > that uses a 48MHz or 64MHz clock to drive the pch_uart. I've found that if I > force the uart_clock to 48MHz (or 64MHz on the latest rev) I can get the kernel > messages and getty on the serial port. > > I see that the the CM-iTC board is special-cased to set a 192MHz uart_clock. > This is done in pch_uart.c code, but there is some register manipulation done in > the pch_phub.c driver and I don't understand the connection. How are the two > related? > > Is the pch_phub.c register manipulation required for proper related? It seems to > work without touching those registers if I just force the clock. > > The device I'm working with is EFI, and the dmi_get_system_info(DMI_BOARD_NAME) > returns "(null)", so I can't use the same test to identify this board. Is there > another common mechanism I might be able to use? There's no relevant DMI information for the board at all? What does: grep . /sys/class/dmi/id/* show? > > The following patch (by way of example, not meant for inclusion) gets things > working for this particular board with this command line: > > console=ttyPCH1,115200 pch_uart.clock_param=48000000 > > I believe the right thing to do here is to discover a way to identify the board > and special case the clock as is done for the CM-iTC, but I would like to > understand the purpose of the pch_phub register manipulation code. Does this > make sense? > > Thanks, > > Darren > > > >From f83fa6cb575844d8e37f136890fe32258eb88dd2 Mon Sep 17 00:00:00 2001 > Message-Id: <f83fa6cb575844d8e37f136890fe32258eb88dd2.1329439822.git.dvhart@xxxxxxxxxxxxxxx> > From: Darren Hart <dvhart@xxxxxxxxxxxxxxx> > Date: Wed, 15 Feb 2012 15:44:18 -0800 > Subject: [PATCH] pch_uart: Add clock parameter > > Allow for the specification of the clock as a module parameter. This is useful > when a board uses a non-standard clock, or when different versions of a board > use different clocks, and that board name or the version are not available to > the kernel. You also rename base_baud to uart_clock here, so you might want to mention it in the changelog entry :) greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
