linux-kernel - [PATCH 2/3] drm/omap: Hide sparse warnings

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Message-Id: <20240806-omapdrm-misc-fixes-v1-2-15d31aea0831@ideasonboard.com>
Date: Tue, 06 Aug 2024 16:50:28 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
 Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Sebastian Reichel <sebastian.reichel@...labora.com>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, 
 kernel test robot <lkp@...el.com>, 
 Ville Syrjälä <ville.syrjala@...ux.intel.com>
Subject: [PATCH 2/3] drm/omap: Hide sparse warnings

sparse reports:

drivers/gpu/drm/omapdrm/omap_dmm_tiler.c:122:16: warning: incorrect type in argument 1 (different address spaces)
drivers/gpu/drm/omapdrm/omap_dmm_tiler.c:122:16:    expected void const volatile [noderef] __iomem *addr
drivers/gpu/drm/omapdrm/omap_dmm_tiler.c:122:16:    got unsigned int [usertype] *wa_dma_data
drivers/gpu/drm/omapdrm/omap_dmm_tiler.c:130:9: warning: incorrect type in argument 2 (different address spaces)
drivers/gpu/drm/omapdrm/omap_dmm_tiler.c:130:9:    expected void volatile [noderef] __iomem *addr
drivers/gpu/drm/omapdrm/omap_dmm_tiler.c:130:9:    got unsigned int [usertype] *wa_dma_data
drivers/gpu/drm/omapdrm/omap_dmm_tiler.c:414:9: warning: incorrect type in argument 1 (different address spaces)
drivers/gpu/drm/omapdrm/omap_dmm_tiler.c:414:9:    expected void const volatile [noderef] __iomem *addr
drivers/gpu/drm/omapdrm/omap_dmm_tiler.c:414:9:    got unsigned int *

These come from pieces of code which do essentially:

p = dma_alloc_coherent()

dma_transfer_to_p()
readl(p)

writel(x, p)
dma_transfer_from_p()

I think we would do just fine without readl() and writel(), accessing
the memory without any extras, but ensuring that the necessary barriers
are in place. But this code is for a legacy platform, has been working
for ages, and it's doing work-arounds for hardware issues, and those
hardware issues are very difficult to trigger... So I would just rather
leave the code be as it is now.

However, the warnings are not nice. Hide the warnings by a (__iomem void
*) typecast.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202407311737.VsJ0Sr1w-lkp@intel.com/
Cc: Ville Syrjälä <ville.syrjala@...ux.intel.com>
---
 drivers/gpu/drm/omapdrm/omap_dmm_tiler.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
index 1aca3060333e..fcd600024136 100644
--- a/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
+++ b/drivers/gpu/drm/omapdrm/omap_dmm_tiler.c
@@ -119,7 +119,7 @@ static u32 dmm_read_wa(struct dmm *dmm, u32 reg)
 	 * earlier than the DMA finished writing the value to memory.
 	 */
 	rmb();
-	return readl(dmm->wa_dma_data);
+	return readl((__iomem void *)dmm->wa_dma_data);
 }
 
 static void dmm_write_wa(struct dmm *dmm, u32 val, u32 reg)
@@ -127,7 +127,7 @@ static void dmm_write_wa(struct dmm *dmm, u32 val, u32 reg)
 	dma_addr_t src, dst;
 	int r;
 
-	writel(val, dmm->wa_dma_data);
+	writel(val, (__iomem void *)dmm->wa_dma_data);
 	/*
 	 * As per i878 workaround, the DMA is used to access the DMM registers.
 	 * Make sure that the writel is not moved by the compiler or the CPU, so
@@ -411,7 +411,7 @@ static int dmm_txn_commit(struct dmm_txn *txn, bool wait)
 	 */
 
 	/* read back to ensure the data is in RAM */
-	readl(&txn->last_pat->next_pa);
+	readl((__iomem void *)&txn->last_pat->next_pa);
 
 	/* write to PAT_DESCR to clear out any pending transaction */
 	dmm_write(dmm, 0x0, reg[PAT_DESCR][engine->id]);

-- 
2.43.0