From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mout.kundenserver.de ([212.227.17.24]:63857 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750768AbbJELH6 (ORCPT ); Mon, 5 Oct 2015 07:07:58 -0400 From: Arnd Bergmann To: Sylwester Nawrocki Cc: Mauro Carvalho Chehab , linux-arm-kernel@lists.infradead.org, Linux Media Mailing List , Krzysztof Kozlowski , linux-samsung-soc@vger.kernel.org, Kyungmin Park , Kukjin Kim Subject: Re: [PATCH 5/7] [media] mipi-csis: make sparse happy Date: Mon, 05 Oct 2015 13:07:20 +0200 Message-ID: <30256208.KbAtSBWnKO@wuerfel> In-Reply-To: <56124FE8.8070400@samsung.com> References: <4962836.RxBJeKxGZM@wuerfel> <56124FE8.8070400@samsung.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-media-owner@vger.kernel.org List-ID: On Monday 05 October 2015 12:24:40 Sylwester Nawrocki wrote: > On 03/10/15 00:25, Arnd Bergmann wrote: > > On Thursday 01 October 2015 19:17:27 Mauro Carvalho Chehab wrote: > >> > diff --git a/drivers/media/platform/exynos4-is/mipi-csis.c b/drivers/media/platform/exynos4-is/mipi-csis.c > >> > index d74e1bec3d86..4b85105dc159 100644 > >> > --- a/drivers/media/platform/exynos4-is/mipi-csis.c > >> > +++ b/drivers/media/platform/exynos4-is/mipi-csis.c > >> > @@ -706,7 +706,8 @@ static irqreturn_t s5pcsis_irq_handler(int irq, void *dev_id) > >> > else > >> > offset = S5PCSIS_PKTDATA_ODD; > >> > > >> > - memcpy(pktbuf->data, state->regs + offset, pktbuf->len); > >> > + memcpy(pktbuf->data, (u8 __force *)state->regs + offset, > >> > + pktbuf->len); > >> > pktbuf->data = NULL; > >> > > > > > I think this is what memcpy_toio() is meant for. > > Exactly memcpy_fromio(). But it's implementation is inefficient on > ARCH=arm, memcpy_fromio() will be translated to a loop of readb(), > only if an arm sub-architecture provides a processor instruction > to access memory by byte. Each readb() also involves a memory barrier. > That's all what we wanted to avoid. AFAIR using memcpy_fromio() was > causing increase of the copy operation several times comparing to > memcpy(). On arm64 it looks better, but this driver is currently > used only on arm32. > > I would prefer to add (void __force *) instead: > > memcpy(pktbuf->data, (void __force *)state->regs + offset, pktbuf->len); > > Alternatively, the memset could just be replaced by a loop of > u32 reads - __raw_readl(); You are right for old kernels, but this was fixed in 7ddfe625cb ("ARM: optimize memset_io()/memcpy_fromio()/memcpy_toio()") at least for little-endian kernels and should be fine now on ARM just like everywhere else. Arnd