From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Subject: Re: [PATCH 02/14] ARM: ARMv7M: Enlarge vector table to 256 entries Date: Fri, 13 Feb 2015 11:00:50 +0100 Message-ID: <20150213100050.GM10842@pengutronix.de> References: <1423763164-5606-1-git-send-email-mcoquelin.stm32@gmail.com> <1423763164-5606-3-git-send-email-mcoquelin.stm32@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-gpio-owner@vger.kernel.org To: Maxime Coquelin Cc: Geert Uytterhoeven , Jonathan Corbet , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Philipp Zabel , Russell King , Daniel Lezcano , Thomas Gleixner , Linus Walleij , Greg Kroah-Hartman , Jiri Slaby , Arnd Bergmann , Andrew Morton , "David S. Miller" , Mauro Carvalho Chehab , Joe Perches , Antti Palosaari , Tejun Heo , Will Deacon , Nikolay Borisov R List-Id: linux-api@vger.kernel.org On Fri, Feb 13, 2015 at 09:42:46AM +0100, Maxime Coquelin wrote: > Hi Geert, >=20 > 2015-02-12 21:34 GMT+01:00 Geert Uytterhoeven : > > On Thu, Feb 12, 2015 at 6:45 PM, Maxime Coquelin > > wrote: > >> From Cortex-M4 and M7 reference manuals, the nvic supports up to 2= 40 > >> interrupts. So the number of entries in vectors table is 256. > >> > >> This patch adds the missing entries, and change the alignement, so= that > >> vector_table remains naturally aligned. > > > > Shouldn't this depend on ARCH_STM32, or some other M4 or M7 specifi= c > > Kconfig option, to avoid wasting the space on other CPUs? >=20 > Actually, the STM32F429 has 90 interrupts, so it would need 106 > entries in the vector table. > The maximum of supported interrupts is not only for Cortex-M4 and M7, > this is also true for Cortex-M3. >=20 > I see two possibilities: > 1 - We declare the vector table for the maximum supported number of > IRQs, as this patch does. > - Pro: it will be functionnal with all Cortex-M MCUs > - Con: Waste of less than 1KB for memory > 2 - We introduce a config flag that provides the number of interrupt= s > - Pro: No more memory waste > - Con: Need to declare a per MCU model config flag. I'd vote for 2, something like: config CPUV7M_NUM_IRQ int default 90 if STM32F429 default 38 if EFM32GG default 240 then there is a working default and platforms being short on memory can configure as appropriate. (The only down side is that if we create multi-platfrom images at some time in the future either all or none of the supported platforms must provide a value here.) =20 > Then, regarding the natural alignment, is there a way to ensure it > depending on the value of a config flag? The exact wording in ARMARMv7-M is: The Vector table must be naturally aligned to a power of two whose alignment value is greater than or equal to (Number of Exceptions supported x 4), with a minimum alignment of 128 bytes. > Or we should keep it at the maximum value possible? So we need: .align x with x being max(7, ceil(log((CPUV7M_NUM_IRQ + 16) * 4, 2))). So the alignment needed is between 7 and 10. If the assembler supports an expression here I'd use that. But before adding strange hacks to generate the right value there better go for a static value like: /* The vector table must be naturally aligned */ #if CONFIG_CPUV7M_NUM_IRQ <=3D 112 .align 9 /* log2((112 + 16) * 4) */ #else .align 10 #endif =46urther steps would be: CONFIG_CPUV7M_NUM_IRQ <=3D 48 -> .align 8 CONFIG_CPUV7M_NUM_IRQ <=3D 16 -> .align 7 Probably it's not worth to add the respective #ifdefs here. Best regards Uwe --=20 Pengutronix e.K. | Uwe Kleine-K=F6nig = | Industrial Linux Solutions | http://www.pengutronix.de/= | -- To unsubscribe from this list: send the line "unsubscribe linux-gpio" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html