From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH 05/15] musb: Do not use musb_read[b|w] / _write[b|w] wrappers in generic fifo functions Date: Tue, 10 Mar 2015 09:50:44 +0100 Message-ID: <11429972.krcjty7oKd@wuerfel> References: <1425933628-9672-1-git-send-email-hdegoede@redhat.com> <4821047.1nqnop93Xh@wuerfel> <54FEA09A.6040401@redhat.com> Reply-To: linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: In-Reply-To: <54FEA09A.6040401-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> List-Post: , List-Help: , List-Archive: , List-Unsubscribe: , To: Hans de Goede Cc: Felipe Balbi , Kishon Vijay Abraham I , Maxime Ripard , Chen-Yu Tsai , Roman Byshko , linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, devicetree , linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org List-Id: devicetree@vger.kernel.org On Tuesday 10 March 2015 08:43:22 Hans de Goede wrote: > On 09-03-15 22:50, Arnd Bergmann wrote: > > On Monday 09 March 2015 21:40:18 Hans de Goede wrote: > >> The generic fifo functions already use non wrapped accesses in various > >> cases through the iowrite#_rep functions, and all platforms which override > >> the default musb_read[b|w] / _write[b|w] functions also provide their own > >> fifo access functions, so we can safely drop the unnecessary indirection > >> from the fifo access functions. > >> > >> Signed-off-by: Hans de Goede > >> > > > > The patch looks reasonably, but the description seem misleading. > > I believe the real reason why it's ok to use __raw_writew for the > > FIFO is that a FIFO by definition is using CPU endian access for > > copying byte streams from memory, which is unlike any other MMIO > > register that requires fixed-endian accessors. > > I'm not sure that that is the case here, this fifo allows reading > 4 bytes at a time using 32 bit word access, so endianness may come > into play. This patch is safe however since all existing users of > the generic fifo_read / write helpers which this patch touches, are > also using the generic musb_read[b|w] / _write[b|w] functions which > are just __raw_foo wrappers, so there is no functional change, which > is what the commit message tries to say. This probably means that the generic musb helpers are not safe to use on big-endian ARM systems (but may work on MIPS). The only one currently not using the generic helpers is blackfin, which is fixed to little endian. > Note that sunxi needs this function because of the register address > translation the sunxi_musb_readb / writeb wrappers are doing which > does not know how to deal with fifo data, and besides that it should > make the generic read / write fifo helpers somewhat faster by removing > an indirect function call. Your sunxi_musb_readw/writew functions however also are endian-safe and seem to get this part right, unlike all other platforms that use the generic __raw_*() accessors. With this patch applied, it should actually work fine, and it would work on other platforms as well if we change all __raw_*() calls outside of musb_default_write_fifo() and musb_default_read_fifo() to use *_relaxed() instead. Arnd