linux-kernel - [PATCH v6 1/7] drm/tilcdc: ensure nonatomic iowrite64 is not used

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Message-Id: <20170803183018.5889-2-logang@deltatee.com>
Date:   Thu,  3 Aug 2017 12:30:12 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-ntb@...glegroups.com, linux-crypto@...r.kernel.org
Cc:     Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Horia Geantă <horia.geanta@....com>,
        Stephen Bates <sbates@...thlin.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Jyri Sarha <jsarha@...com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        David Airlie <airlied@...ux.ie>
Subject: [PATCH v6 1/7] drm/tilcdc: ensure nonatomic iowrite64 is not used

Add a check to ensure iowrite64 is only used if it is atomic.

It was decided in [1] that the tilcdc driver should not be using an
atomic operation (so it was left out of this patchset). However, it turns
out that through the drm code, a nonatomic header is actually included:

include/linux/io-64-nonatomic-lo-hi.h
is included from include/drm/drm_os_linux.h:9:0,
            from include/drm/drmP.h:74,
            from include/drm/drm_modeset_helper.h:26,
            from include/drm/drm_atomic_helper.h:33,
            from drivers/gpu/drm/tilcdc/tilcdc_crtc.c:19:

And thus, without this change, this patchset would inadvertantly
change the behaviour of the tilcdc driver.

[1] lkml.kernel.org/r/CAK8P3a2HhO_zCnsTzq7hmWSz5La5Thu19FWZpun16iMnyyNreQ@...l.gmail.com

Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
Cc: Jyri Sarha <jsarha@...com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Tomi Valkeinen <tomi.valkeinen@...com>
Cc: David Airlie <airlied@...ux.ie>
---
 drivers/gpu/drm/tilcdc/tilcdc_regs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/tilcdc/tilcdc_regs.h b/drivers/gpu/drm/tilcdc/tilcdc_regs.h
index 9d528c0a67a4..5048ebb86835 100644
--- a/drivers/gpu/drm/tilcdc/tilcdc_regs.h
+++ b/drivers/gpu/drm/tilcdc/tilcdc_regs.h
@@ -133,7 +133,7 @@ static inline void tilcdc_write64(struct drm_device *dev, u32 reg, u64 data)
 	struct tilcdc_drm_private *priv = dev->dev_private;
 	volatile void __iomem *addr = priv->mmio + reg;
 
-#ifdef iowrite64
+#if defined(iowrite64) && !defined(iowrite64_is_nonatomic)
 	iowrite64(data, addr);
 #else
 	__iowmb();
-- 
2.11.0