From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:6f8:1178:4:290:27ff:fe1d:cc33]) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1UEopk-0000K2-N5 for barebox@lists.infradead.org; Sun, 10 Mar 2013 22:35:13 +0000 Date: Sun, 10 Mar 2013 23:35:10 +0100 From: Sascha Hauer Message-ID: <20130310223510.GR1906@pengutronix.de> References: <1362871182-25726-1-git-send-email-vicencb@gmail.com> <1362871182-25726-5-git-send-email-vicencb@gmail.com> <20130310131601.GA11170@game.jcrosoft.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH 4/9] omap_uart: add low level port serial initialization To: vj Cc: barebox@lists.infradead.org On Sun, Mar 10, 2013 at 11:16:00PM +0100, vj wrote: > On Sun, Mar 10, 2013 at 2:16 PM, Jean-Christophe PLAGNIOL-VILLARD > wrote: > > On 00:19 Sun 10 Mar , Vicente Bergas wrote: > >> some sort of UART setup has to be done in order to use PUTC_LL > >> > >> Signed-off-by: Vicente Bergas > >> --- > >> arch/arm/mach-omap/include/mach/debug_ll.h | 21 +++++++++++++++++++++ > >> 1 file changed, 21 insertions(+) > >> > >> diff --git a/arch/arm/mach-omap/include/mach/debug_ll.h b/arch/arm/mach-omap/include/mach/debug_ll.h > >> index eea6eb3..9740848 100644 > >> --- a/arch/arm/mach-omap/include/mach/debug_ll.h > >> +++ b/arch/arm/mach-omap/include/mach/debug_ll.h > >> @@ -45,9 +45,30 @@ > >> #endif > >> > >> #define LSR_THRE 0x20 /* Xmit holding register empty */ > >> +#define LCR_BKSE 0x80 /* Bank select enable */ > >> #define LSR (5 << 2) > >> #define THR (0 << 2) > >> +#define DLL (0 << 2) > >> +#define IER (1 << 2) > >> +#define DLM (1 << 2) > >> +#define FCR (2 << 2) > >> +#define LCR (3 << 2) > >> +#define MCR (4 << 2) > >> +#define MDR (8 << 2) > >> > >> +static inline void INIT_LL(void) > > where this come from? > > This comes from drivers/serial/serial_ns16550.c: ns16550_serial_init_port > ns16550_serial_init_port call other functions and has local variables, > so a stack is required > INIT_LL instead is an extremly simple inline function without local > variables, so it can be called at the very beginning > > from include/debug_ll.h: > "Note that several SoCs expect the UART to be initialized by a > debugger or a first stage bootloader." > INIT_LL implements the second option. > > I have a question regarding code executed at the very beginning, that > is, when the stack may not be available or the binary is not at it's > link address > What are the things that can't be done in such scenario? > For example, from include/debug_ll.h: > "Be careful with PUTS_LL, it only works if the binary is running at > the link address which often is not the case during early startup." > static __inline__ void PUTS_LL(const char * str) > { > while (*str) { > if (*str == '\n') { > PUTC_LL('\r'); > } > PUTC_LL(*str); > str++; > } > } > What does PUTS_LL do that can't be done? You can't access global variables at that state. They are addressed with their absolute address which will not be correct when you are not running at the linked address. You can simply verify that by doing a PUTHEX_LL("somestring"); You will see the address the string is located when running from the correct address. Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox