From:   Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To:     linux-efi@vger.kernel.org, mika.westerberg@linux.intel.com
Cc:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Alexander Graf <agraf@suse.de>,
        Matt Fleming <matt@codeblueprint.co.uk>
Subject: [PATCH v1] efi/earlycon: Remap entire framebuffer after page initialization
Date:   Mon, 11 Nov 2019 17:44:13 +0200
Message-Id: <20191111154413.1505-1-andriy.shevchenko@linux.intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-efi-owner@vger.kernel.org
Precedence: bulk

When the commit 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk
into generic earlycon implementation") moved x86 specific EFI earlyprintk
implementation to shared location it also tweaked the behaviour. In particular
it dropped a trick with full framebuffer remapping after page initialization.
This lead to two regressions:
1) very slow scrolling after page initialization;
2) kernel hang when keep_bootcon parameter is being provided.

Returning the trick back fixes #2 and mitigates, i.e. reduces the window when
slowness appears, #1 presumably due to eliminating heavy map()/unmap()
operations per each pixel line on the screen.

Fixes: 69c1f396f25b ("efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation")
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Alexander Graf <agraf@suse.de>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/firmware/efi/earlycon.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/firmware/efi/earlycon.c b/drivers/firmware/efi/earlycon.c
index c9a0efca17b0..ddb6c0ff2553 100644
--- a/drivers/firmware/efi/earlycon.c
+++ b/drivers/firmware/efi/earlycon.c
@@ -17,14 +17,47 @@ static const struct font_desc *font;
 static u32 efi_x, efi_y;
 static u64 fb_base;
 static pgprot_t fb_prot;
+static void *efi_fb;
+
+/*
+ * efi earlycon needs to use early_memremap() to map the framebuffer.
+ * But early_memremap() is not usable for 'earlycon=efifb keep_bootcon',
+ * memremap() should be used instead. memremap() will be available after
+ * paging_init() which is earlier than initcall callbacks. Thus adding this
+ * early initcall function early_efi_map_fb() to map the whole efi framebuffer.
+ */
+static __init int early_efi_map_fb(void)
+{
+	u32 size;
+
+	size = screen_info.lfb_size;
+	if (pgprot_val(fb_prot) == pgprot_val(PAGE_KERNEL))
+		efi_fb = memremap(fb_base, size, MEMREMAP_WB);
+	else
+		efi_fb = memremap(fb_base, size, MEMREMAP_WC);
+
+	return efi_fb ? 0 : -ENOMEM;
+}
+early_initcall(early_efi_map_fb);
+
+static __exit void early_efi_unmap_fb(void)
+{
+	memunmap(efi_fb);
+}
 
 static __ref void *efi_earlycon_map(unsigned long start, unsigned long len)
 {
+	if (efi_fb)
+		return efi_fb + start;
+
 	return early_memremap_prot(fb_base + start, len, pgprot_val(fb_prot));
 }
 
 static __ref void efi_earlycon_unmap(void *addr, unsigned long len)
 {
+	if (efi_fb)
+		return;
+
 	early_memunmap(addr, len);
 }
 
-- 
2.24.0.rc1