linux-kernel - [PATCH] Remove unnecessary calls to kmap{,_local_page}() when acquiring pages using GFP

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Date:   Wed, 19 Jul 2023 06:43:14 -0700
From:   Sumitra Sharma <sumitraartsy@...il.com>
To:     Patrik Jakobsson <patrik.r.jakobsson@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Ira Weiny <ira.weiny@...el.com>,
        Fabio <fmdefrancesco@...il.com>, Deepak R Varma <drv@...lo.com>,
        Sumitra Sharma <sumitraartsy@...il.com>,
        Alison Schofield <alison.schofield@...el.com>
Subject: [PATCH] Remove unnecessary calls to kmap{,_local_page}() when
 acquiring pages using GFP_DMA32.

The GFP_DMA32 uses the DMA32 zone to satisfy the allocation
requests. Therefore, pages allocated with GFP_DMA32 cannot
come from Highmem.

Avoid using calls to kmap() / kunmap() as the kmap() is being
deprecated [1].

Avoid using calls to kmap_local_page() / kunmap_local() as the
code does not depends on the implicit disable of migration of
local mappings and is, in fact, an unnecessary overhead for
the main code [2].

Hence, use a plain page_address() directly in the
psb_mmu_alloc_pd function.

[1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com/
[2]: https://lwn.net/Articles/836503/

Suggested-by: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Sumitra Sharma <sumitraartsy@...il.com>
---
 drivers/gpu/drm/gma500/mmu.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/gma500/mmu.c b/drivers/gpu/drm/gma500/mmu.c
index a70b01ccdf70..1a44dd062fd1 100644
--- a/drivers/gpu/drm/gma500/mmu.c
+++ b/drivers/gpu/drm/gma500/mmu.c
@@ -184,20 +184,15 @@ struct psb_mmu_pd *psb_mmu_alloc_pd(struct psb_mmu_driver *driver,
 		pd->invalid_pte = 0;
 	}
 
-	v = kmap_local_page(pd->dummy_pt);
+	v = page_address(pd->dummy_pt);
 	for (i = 0; i < (PAGE_SIZE / sizeof(uint32_t)); ++i)
 		v[i] = pd->invalid_pte;
 
-	kunmap_local(v);
-
-	v = kmap_local_page(pd->p);
+	v = page_address(pd->p);
 	for (i = 0; i < (PAGE_SIZE / sizeof(uint32_t)); ++i)
 		v[i] = pd->invalid_pde;
 
-	kunmap_local(v);
-
-	clear_page(kmap(pd->dummy_page));
-	kunmap(pd->dummy_page);
+	clear_page(page_address(pd->dummy_page));
 
 	pd->tables = vmalloc_user(sizeof(struct psb_mmu_pt *) * 1024);
 	if (!pd->tables)
-- 
2.25.1