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

[Hans Verkuil <hverkuil@xxxxxxxxx>]

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 SyrjÃlà <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 Monnà <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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