linux-kernel - [PATCH 4.15 30/84] drm/tilcdc: ensure nonatomic iowrite64 is not used

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Date:   Fri, 23 Mar 2018 10:53:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Logan Gunthorpe <logang@...tatee.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Jyri Sarha <jsarha@...com>, Arnd Bergmann <arnd@...db.de>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        David Airlie <airlied@...ux.ie>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.15 30/84] drm/tilcdc: ensure nonatomic iowrite64 is not used

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Logan Gunthorpe <logang@...tatee.com>


[ Upstream commit 4e5ca2d930aa8714400aedf4bf1dc959cb04280f ]

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>
Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Jyri Sarha <jsarha@...com>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Tomi Valkeinen <tomi.valkeinen@...com>
Cc: David Airlie <airlied@...ux.ie>
Signed-off-by: Jyri Sarha <jsarha@...com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/tilcdc/tilcdc_regs.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- 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
 	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();