Re: [PATCH v6 1/3] ivtv: use arch_phys_wc_add() and require PAT disabled

From: Hans Verkuil
Date: Tue Jun 09 2015 - 02:24:30 EST

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On 06/09/2015 02:56 AM, Mauro Carvalho Chehab wrote:
> Em Mon, 08 Jun 2015 17:20:20 -0700
> "Luis R. Rodriguez" <mcgrof@xxxxxxxxxxxxxxxx> escreveu:
>
>> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
>>
>> We are burrying direct access to MTRR code support on
>> x86 in order to take advantage of PAT. In the future we
>> also want to make the default behaviour of ioremap_nocache()
>> to use strong UC, use of mtrr_add() on those systems
>> would make write-combining void.
>>
>> In order to help both enable us to later make strong
>> UC default and in order to phase out direct MTRR access
>> code port the driver over to arch_phys_wc_add() and
>> annotate that the device driver requires systems to
>> boot with PAT disabled, with the nopat kernel parameter.
>>
>> This is a worthy comprmise given that the hardware is
>> really rare these days, and perhaps only some lost souls
>> in some third world country are expected to be using this
>> feature of the device driver.
>>
>> Acked-by: Andy Walls <awalls@xxxxxxxxxxxxxxxx>
>> Cc: Andy Walls <awalls@xxxxxxxxxxxxxxxx>
>> Cc: Doug Ledford <dledford@xxxxxxxxxx>
>> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>
>
> Provided that you fix the issues below:
> Acked-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxxxx>
>
>> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>> Cc: Suresh Siddha <sbsiddha@xxxxxxxxx>
>> Cc: Ingo Molnar <mingo@xxxxxxx>
>> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> Cc: Juergen Gross <jgross@xxxxxxxx>
>> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
>> Cc: Dave Airlie <airlied@xxxxxxxxxx>
>> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>> Cc: Antonino Daplas <adaplas@xxxxxxxxx>
>> Cc: Jean-Christophe Plagniol-Villard <plagnioj@xxxxxxxxxxxx>
>> Cc: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
>> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
>> Cc: Arnd Bergmann <arnd@xxxxxxxx>
>> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
>> Cc: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
>> Cc: Ville SyrjÃlÃ <syrjala@xxxxxx>
>> Cc: Mel Gorman <mgorman@xxxxxxx>
>> Cc: Vlastimil Babka <vbabka@xxxxxxx>
>> Cc: Borislav Petkov <bp@xxxxxxx>
>> Cc: Davidlohr Bueso <dbueso@xxxxxxx>
>> Cc: konrad.wilk@xxxxxxxxxx
>> Cc: ville.syrjala@xxxxxxxxxxxxxxx
>> Cc: david.vrabel@xxxxxxxxxx
>> Cc: jbeulich@xxxxxxxx
>> Cc: toshi.kani@xxxxxx
>> Cc: Roger Pau MonnÃ <roger.pau@xxxxxxxxxx>
>> Cc: linux-fbdev@xxxxxxxxxxxxxxx
>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>> Cc: ivtv-devel@xxxxxxxxxxxxxx
>> Cc: linux-media@xxxxxxxxxxxxxxx
>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
>> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx>
>> ---
>> drivers/media/pci/ivtv/Kconfig | 3 +++
>> drivers/media/pci/ivtv/ivtvfb.c | 58 ++++++++++++++++-------------------------
>> 2 files changed, 26 insertions(+), 35 deletions(-)
>>
>> diff --git a/drivers/media/pci/ivtv/Kconfig b/drivers/media/pci/ivtv/Kconfig
>> index dd6ee57e..b2a7f88 100644
>> --- a/drivers/media/pci/ivtv/Kconfig
>> +++ b/drivers/media/pci/ivtv/Kconfig
>> @@ -57,5 +57,8 @@ config VIDEO_FB_IVTV
>> This is used in the Hauppauge PVR-350 card. There is a driver
>> homepage at <http://www.ivtvdriver.org>.
>>
>> + If you have this hardware you will need to boot with PAT disabled
>> + on your x86 systems, use the nopat kernel parameter.
>> +
>
> Hmm... FB_IVTV is not hardware... it is framebuffer support for IVTV.
> It is optional to use FB API for the video output port of this board,
> instead of using V4L2 API.

That's not true. It is hardware: it drives the video output OSD which overlays
the video output. The reason it is optional is that it is hard to unload a
framebuffer module and most people don't need it.

So V4L2 drives the video output and ivtvfb drives the OSD overlay. So it is
not a case of 'instead of'.

>
> I would say, instead, something like:
>
> "In order to use this module, you will need to boot with PAT disabled
> on x86 systems, using the nopat kernel parameter."

I do agree with this change, but that's because this module is optional and
not for the reasons you mentioned above.

Regards,

Hans

>
>> To compile this driver as a module, choose M here: the
>> module will be called ivtvfb.
>> diff --git a/drivers/media/pci/ivtv/ivtvfb.c b/drivers/media/pci/ivtv/ivtvfb.c
>> index 9ff1230..7685ae3 100644
>> --- a/drivers/media/pci/ivtv/ivtvfb.c
>> +++ b/drivers/media/pci/ivtv/ivtvfb.c
>> @@ -44,8 +44,8 @@
>> #include <linux/ivtvfb.h>
>> #include <linux/slab.h>
>>
>> -#ifdef CONFIG_MTRR
>> -#include <asm/mtrr.h>
>> +#ifdef CONFIG_X86_64
>> +#include <asm/pat.h>
>> #endif
>>
>> #include "ivtv-driver.h"
>> @@ -155,12 +155,11 @@ struct osd_info {
>> /* Buffer size */
>> u32 video_buffer_size;
>>
>> -#ifdef CONFIG_MTRR
>> /* video_base rounded down as required by hardware MTRRs */
>> unsigned long fb_start_aligned_physaddr;
>> /* video_base rounded up as required by hardware MTRRs */
>> unsigned long fb_end_aligned_physaddr;
>> -#endif
>> + int wc_cookie;
>>
>> /* Store the buffer offset */
>> int set_osd_coords_x;
>> @@ -1099,6 +1098,8 @@ static int ivtvfb_init_vidmode(struct ivtv *itv)
>> static int ivtvfb_init_io(struct ivtv *itv)
>> {
>> struct osd_info *oi = itv->osd_info;
>> + /* Find the largest power of two that maps the whole buffer */
>> + int size_shift = 31;
>>
>> mutex_lock(&itv->serialize_lock);
>> if (ivtv_init_on_first_open(itv)) {
>> @@ -1132,29 +1133,16 @@ static int ivtvfb_init_io(struct ivtv *itv)
>> oi->video_pbase, oi->video_vbase,
>> oi->video_buffer_size / 1024);
>>
>> -#ifdef CONFIG_MTRR
>> - {
>> - /* Find the largest power of two that maps the whole buffer */
>> - int size_shift = 31;
>> -
>> - while (!(oi->video_buffer_size & (1 << size_shift))) {
>> - size_shift--;
>> - }
>> - size_shift++;
>> - oi->fb_start_aligned_physaddr = oi->video_pbase & ~((1 << size_shift) - 1);
>> - oi->fb_end_aligned_physaddr = oi->video_pbase + oi->video_buffer_size;
>> - oi->fb_end_aligned_physaddr += (1 << size_shift) - 1;
>> - oi->fb_end_aligned_physaddr &= ~((1 << size_shift) - 1);
>> - if (mtrr_add(oi->fb_start_aligned_physaddr,
>> - oi->fb_end_aligned_physaddr - oi->fb_start_aligned_physaddr,
>> - MTRR_TYPE_WRCOMB, 1) < 0) {
>> - IVTVFB_INFO("disabled mttr\n");
>> - oi->fb_start_aligned_physaddr = 0;
>> - oi->fb_end_aligned_physaddr = 0;
>> - }
>> - }
>> -#endif
>> -
>> + while (!(oi->video_buffer_size & (1 << size_shift)))
>> + size_shift--;
>> + size_shift++;
>> + oi->fb_start_aligned_physaddr = oi->video_pbase & ~((1 << size_shift) - 1);
>> + oi->fb_end_aligned_physaddr = oi->video_pbase + oi->video_buffer_size;
>> + oi->fb_end_aligned_physaddr += (1 << size_shift) - 1;
>> + oi->fb_end_aligned_physaddr &= ~((1 << size_shift) - 1);
>> + oi->wc_cookie = arch_phys_wc_add(oi->fb_start_aligned_physaddr,
>> + oi->fb_end_aligned_physaddr -
>> + oi->fb_start_aligned_physaddr);
>> /* Blank the entire osd. */
>> memset_io(oi->video_vbase, 0, oi->video_buffer_size);
>>
>> @@ -1172,14 +1160,7 @@ static void ivtvfb_release_buffers (struct ivtv *itv)
>>
>> /* Release pseudo palette */
>> kfree(oi->ivtvfb_info.pseudo_palette);
>> -
>> -#ifdef CONFIG_MTRR
>> - if (oi->fb_end_aligned_physaddr) {
>> - mtrr_del(-1, oi->fb_start_aligned_physaddr,
>> - oi->fb_end_aligned_physaddr - oi->fb_start_aligned_physaddr);
>> - }
>> -#endif
>> -
>> + arch_phys_wc_del(oi->wc_cookie);
>> kfree(oi);
>> itv->osd_info = NULL;
>> }
>> @@ -1284,6 +1265,13 @@ static int __init ivtvfb_init(void)
>> int registered = 0;
>> int err;
>>
>> +#ifdef CONFIG_X86_64
>> + if (WARN(pat_enabled(),
>> + "ivtvfb needs PAT disabled, boot with nopat kernel parameter\n")) {
>> + return EINVAL;
>
> Errors are always negative. So:
> return -EINVAL
>
> Or, perhaps, -ENODEV.
>
>> + }
>> +#endif
>> +
>> if (ivtvfb_card_id < -1 || ivtvfb_card_id >= IVTV_MAX_CARDS) {
>> printk(KERN_ERR "ivtvfb: ivtvfb_card_id parameter is out of range (valid range: -1 - %d)\n",
>> IVTV_MAX_CARDS - 1);
> --
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Next message: Christoph Hellwig: "Re: [PATCH v4 1/5] fs: kiocb: introduce IOCB_DONT_DIRTY_PAGE flag for direct IO"
Previous message: Tejun Heo: "Re: [RFC PATCH 02/18] kthread: Add API for iterant kthreads"
In reply to: Mauro Carvalho Chehab: "Re: [PATCH v6 1/3] ivtv: use arch_phys_wc_add() and require PAT disabled"
Next in thread: Luis R. Rodriguez: "[PATCH v6 2/3] IB/ipath: add counting for MTRR"
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