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media: ivtv: add parameter to enable ivtvfb on x86 PAT systems

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ivtvfb was previously disabled for x86 PAT-enabled systems
by commit 1bf1735b47 ("x86/mm/pat, drivers/media/ivtv:
Use arch_phys_wc_add() and require PAT disabled") as a
workaround to abstract MTRR code away from device drivers.

The driver is not easily upgradable to the PAT-aware
ioremap_wc() API since the firmware hides the address
ranges that should be marked write-combined from the driver.
However, since a write-combined cache on the framebuffer
is only a performance enhancement not a requirement for
the framebuffer to function, completely disabling the driver
in this configuration is not necessary.

Add force_pat module parameter and a corresponding kernel
configuration parameter to optionally force initialization
on PAT-enabled x86 systems with a warning about the lack of
write-combined caching, and document the reasons the driver
cannot be easily updated to support wc caching on all systems.

Signed-off-by: Nick French <naf@ou.edu>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
[hverkuil-cisco@xs4all.nl: fix typo, split long pr_ lines up]
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
This commit is contained in:
French, Nicholas A 2018-03-11 16:27:28 -03:00 committed by Mauro Carvalho Chehab
parent dc60a4cfb7
commit 526daee730
2 changed files with 34 additions and 5 deletions
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23
drivers/media/pci/ivtv/Kconfig
View file

@ -70,8 +70,25 @@ config VIDEO_FB_IVTV
This is used in the Hauppauge PVR-350 card. There is a driver
homepage at <http://www.ivtvdriver.org>.
In order to use this module, you will need to boot with PAT disabled
on x86 systems, using the nopat kernel parameter.
To compile this driver as a module, choose M here: the
module will be called ivtvfb.
config VIDEO_FB_IVTV_FORCE_PAT
bool "force cx23415 framebuffer init with x86 PAT enabled"
depends on VIDEO_FB_IVTV && X86_PAT
default n
---help---
With PAT enabled, the cx23415 framebuffer driver does not
utilize write-combined caching on the framebuffer memory.
For this reason, the driver will by default disable itself
when initializied on a kernel with PAT enabled (i.e. not
using the nopat kernel parameter).
The driver is not easily upgradable to the PAT-aware
ioremap_wc() API since the firmware hides the address
ranges that should be marked write-combined from the driver.
With this setting enabled, the framebuffer will initialize on
PAT-enabled systems but the framebuffer memory will be uncached.
If unsure, say N.

16
drivers/media/pci/ivtv/ivtvfb.c
View file

@ -55,6 +55,7 @@
/* card parameters */
static int ivtvfb_card_id = -1;
static int ivtvfb_debug = 0;
static bool ivtvfb_force_pat = IS_ENABLED(CONFIG_VIDEO_FB_IVTV_FORCE_PAT);
static bool osd_laced;
static int osd_depth;
static int osd_upper;
@ -64,6 +65,7 @@ static int osd_xres;
module_param(ivtvfb_card_id, int, 0444);
module_param_named(debug,ivtvfb_debug, int, 0644);
module_param_named(force_pat, ivtvfb_force_pat, bool, 0644);
module_param(osd_laced, bool, 0444);
module_param(osd_depth, int, 0444);
module_param(osd_upper, int, 0444);
@ -79,6 +81,9 @@ MODULE_PARM_DESC(debug,
"Debug level (bitmask). Default: errors only\n"
"\t\t\t(debug = 3 gives full debugging)");
MODULE_PARM_DESC(force_pat,
"Force initialization on x86 PAT-enabled systems (bool).\n");
/* Why upper, left, xres, yres, depth, laced ? To match terminology used
by fbset.
Why start at 1 for left & upper coordinate ? Because X doesn't allow 0 */
@ -1167,8 +1172,15 @@ static int ivtvfb_init_card(struct ivtv *itv)
#ifdef CONFIG_X86_64
if (pat_enabled()) {
pr_warn("ivtvfb needs PAT disabled, boot with nopat kernel parameter\n");
return -ENODEV;
if (ivtvfb_force_pat) {
pr_info("PAT is enabled. Write-combined framebuffer caching will be disabled.\n");
pr_info("To enable caching, boot with nopat kernel parameter\n");
} else {
pr_warn("ivtvfb needs PAT disabled for write-combined framebuffer caching.\n");
pr_warn("Boot with nopat kernel parameter to use caching, or use the\n");
pr_warn("force_pat module parameter to run with caching disabled\n");
return -ENODEV;
}
}
#endif