From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Ungerer Subject: Re: endianness swapped Date: Mon, 29 Apr 2019 17:03:59 +1000 Message-ID: <50f49e95-95f3-4fdb-bcf6-6165382a5168@linux-m68k.org> References: <20190427153222.GA9613@jerusalem> <20190427202150.GB9613@jerusalem> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Arnd Bergmann Cc: Geert Uytterhoeven , Angelo Dureghello , Logan Gunthorpe , Thomas Gleixner , Kate Stewart , Philippe Ombredanne , Greg KH , Linux/m68k , Linux-Arch , Linux Kernel Mailing List List-Id: linux-m68k@vger.kernel.org Hi Arnd, On 29/4/19 4:44 am, Arnd Bergmann wrote: > On Sun, Apr 28, 2019 at 3:59 PM Greg Ungerer wrote: >> On 28/4/19 7:21 pm, Arnd Bergmann wrote: >>> On Sun, Apr 28, 2019 at 10:46 AM Geert Uytterhoeven >>> wrote: >>>> On Sat, Apr 27, 2019 at 10:22 PM Angelo Dureghello wrote: >>>>> On Sat, Apr 27, 2019 at 05:32:22PM +0200, Angelo Dureghello wrote: >>> >>> Coldfire makes the behavior of readw()/readl() depend on the >>> MMIO address, presumably since that was the easiest way to >>> get drivers working originally, but it breaks the assumption >>> in the asm-generic code. >> >> Yes, that is right. >> >> There is a number of common hardware modules that Freescale have >> used in the ColdFire SoC parts and in their ARM based parts (iMX >> families). The ARM parts are pretty much always little endian, and >> the ColdFire is always big endian. The hardware registers in those >> hardware blocks are always accessed in native endian of the processor. > > In later Freescale/NXP ARM SoCs (i.MX and Layerscape), we > also get a lot of devices pulled over from PowerPC, with random > endianess. In some cases, the same device that had big-endian > registers originally ends up in two different ARM products and one of > them uses big-endian while the other one uses little-endian registers. > >> So the address range checks are to deal with those internal >> hardware blocks (i2c, spi, dma, etc), since we know those are >> at fixed addresses. That leaves the usual endian swapping in place for >> other general (ie external) devices (PCI devices, network chips, etc). > > Is there a complete list of coldfire on-chip device drivers? > > Looking at some of the drivers: > > - drivers/i2c/busses/i2c-imx.c uses only 8-bit accesses and works either way, > same for drivers/tty/serial/mcf.c > - drivers/spi/spi-coldfire-qspi.c is apparently coldfire-only and could use > ioread32be for a portable to do big-endian register access. > - edma-common has a wrapper to support both big-endian and little-endian > configurations in the same kernel image, but the mcf interrupt handler > is hardcoded to the (normally) little-endian ioread32 function. > - drivers/net/ethernet/freescale/fec_main.c is shared between coldfire > and i.MX (but not mpc52xx), and is hardcoded to readl/writel, and > would need the same trick as edma to make it portable. That matches up with what we list out in arch/m68k/coldfire/devices.c. I can't think of any other drivers. There is a lot of use readl/writel and friends in the architecture specific code too, in arch/m68k/coldfire. At first I used __raw_readl/ __raw_writel to always get native endianess. But quote a few uses of readl/writel have crept in over the years. Regards Greg