[EXT] Re: [v2 1/3] drm/arm/mali-dp: Add display QoS interface configuration for Mali DP500

Liviu Dudau liviu.dudau at arm.com
Mon Jul 22 09:32:41 UTC 2019 

On Mon, Jul 22, 2019 at 02:12:08AM +0000, Wen He wrote:
> 
> 
> > -----Original Message-----
> > From: Liviu Dudau <liviu.dudau at arm.com>
> > Sent: 2019年7月19日 19:46
> > To: Wen He <wen.he_1 at nxp.com>
> > Cc: dri-devel at lists.freedesktop.org; linux-kernel at vger.kernel.org;
> > brian.starkey at arm.com; airlied at linux.ie; daniel at ffwll.ch; Leo Li
> > <leoyang.li at nxp.com>
> > Subject: [EXT] Re: [v2 1/3] drm/arm/mali-dp: Add display QoS interface
> > configuration for Mali DP500
> > 
> > Caution: EXT Email
> > 
> > On Fri, Jul 19, 2019 at 05:54:45PM +0800, Wen He wrote:
> > > Configure the display Quality of service (QoS) levels priority if the
> > > optional property node "arm,malidp-aqros-value" is defined in DTS file.
> > >
> > > QoS signaling using AQROS and AWQOS AXI interface signals, the AQROS
> > > is driven from the "RQOS" register, so needed to program the RQOS
> > > register to avoid the 4k resolution flicker issue on the LS1028A platform.
> > >
> > > Signed-off-by: Wen He <wen.he_1 at nxp.com>
> > > ---
> > > change in v2:
> > >         - modify some content based on feedback from maintainers
> > >
> > >  drivers/gpu/drm/arm/malidp_drv.c  |  6 ++++++
> > >  drivers/gpu/drm/arm/malidp_hw.c   | 13 +++++++++++++
> > >  drivers/gpu/drm/arm/malidp_hw.h   |  3 +++
> > >  drivers/gpu/drm/arm/malidp_regs.h | 10 ++++++++++
> > >  4 files changed, 32 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/arm/malidp_drv.c
> > > b/drivers/gpu/drm/arm/malidp_drv.c
> > > index f25ec4382277..61c49a0668a7 100644
> > > --- a/drivers/gpu/drm/arm/malidp_drv.c
> > > +++ b/drivers/gpu/drm/arm/malidp_drv.c
> > > @@ -818,6 +818,12 @@ static int malidp_bind(struct device *dev)
> > >
> > >       malidp->core_id = version;
> > >
> > > +     ret = of_property_read_u32(dev->of_node,
> > > +                                     "arm,malidp-arqos-value",
> > > +                                     &hwdev->arqos_value);
> > > +     if (ret)
> > > +             hwdev->arqos_value = 0x0;
> > 
> > Is zero the default value that you want? I thought it was 0x00010001.
> 
> Actually, the register default value always is 0x00010001(can be found in RM document).

Exactly, but with your code you are overwriting it to 0 if the DT doesn't have
the arm,malidp-arqos-value property.

> 
> > 
> > > +
> > >       /* set the number of lines used for output of RGB data */
> > >       ret = of_property_read_u8_array(dev->of_node,
> > >                                       "arm,malidp-output-port-lines",
> > > diff --git a/drivers/gpu/drm/arm/malidp_hw.c
> > > b/drivers/gpu/drm/arm/malidp_hw.c index 50af399d7f6f..323683b1e9f7
> > > 100644
> > > --- a/drivers/gpu/drm/arm/malidp_hw.c
> > > +++ b/drivers/gpu/drm/arm/malidp_hw.c
> > > @@ -374,6 +374,19 @@ static void malidp500_modeset(struct
> > malidp_hw_device *hwdev, struct videomode *
> > >               malidp_hw_setbits(hwdev, MALIDP_DISP_FUNC_ILACED,
> > MALIDP_DE_DISPLAY_FUNC);
> > >       else
> > >               malidp_hw_clearbits(hwdev, MALIDP_DISP_FUNC_ILACED,
> > > MALIDP_DE_DISPLAY_FUNC);
> > > +
> > > +     /*
> > > +      * Program the RQoS register to avoid 4k resolution flicker
> > > +      * on the LS1028A.
> > > +      */
> > > +     if (hwdev->arqos_value) {
> > > +             val = hwdev->arqos_value;
> > > +
> > > +             if (mode->pixelclock == 594000000)
> > 
> > If I remember correctly, you declare the pixelclocks in the device tree, so I
> > wonder if this is needed here. We should just set what value was in the DT
> > regardless of the pixelclock, and then you manipulate the DT to choose one of
> > your fixed resolutions and also set the QoS value.
> 
> Yes, you remember correctly, but
> 1. declare the pixelclocks in the device tree.
> About this, I was hoping to discuss it with you. I want to implement another patch
> that just declare 27MHz reference clock in the device tree and add a fake clock subsystem
> to enable/display prepare to set PLL. I am thinking what to do next.
> As I remember, I sent out a patch that "Disable checking for required pixel clock",
> I think should be cancel it.
> 
> 2. declare the fixed resolutions list in DTS.
> Yes, Although I put four resolutions for supported list in DTS file, but this just a
> workaround that If not enable EDID OR EDID is not available. Once EDID is enabled,
> these resolutions list declare will be remove in DTS. so we can't use it as a condition
> to set the QoS value. 

3. Actually enable the clock provider. I've had a look at the public
documentation and it looks like the the pixelclock is provided by an IDT VersaClock 5
generator, for which there is a kernel driver. I've started playing with it but got 
pulled back by other more immediate tasks.

Anyway, what I was trying to hint was that putting in the code the exact pixelclock
value might not be the best thing. In my view, pixelclock reflects the need for
a certain bandwidth, with is usually a product of output (number of pixels) and
refresh frequency. I'm guessing going above 4k at 60 will also trigger the
flicker, but with your patch we will not react correctly.

Best regards,
Liviu


> 
> Best Regards,
> Wen
> 
> > 
> > Best regards,
> > Liviu
> > 
> > > +                     malidp_hw_setbits(hwdev, val,
> > MALIDP500_RQOS_QUALITY);
> > > +             else
> > > +                     malidp_hw_clearbits(hwdev, val,
> > MALIDP500_RQOS_QUALITY);
> > > +     }
> > >  }
> > >
> > >  int malidp_format_get_bpp(u32 fmt)
> > > diff --git a/drivers/gpu/drm/arm/malidp_hw.h
> > > b/drivers/gpu/drm/arm/malidp_hw.h index 968a65eed371..e4c36bc90bda
> > > 100644
> > > --- a/drivers/gpu/drm/arm/malidp_hw.h
> > > +++ b/drivers/gpu/drm/arm/malidp_hw.h
> > > @@ -251,6 +251,9 @@ struct malidp_hw_device {
> > >
> > >       /* size of memory used for rotating layers, up to two banks available
> > */
> > >       u32 rotation_memory[2];
> > > +
> > > +     /* priority level of RQOS register used for driven the ARQOS signal */
> > > +     u32 arqos_value;
> > >  };
> > >
> > >  static inline u32 malidp_hw_read(struct malidp_hw_device *hwdev, u32
> > > reg) diff --git a/drivers/gpu/drm/arm/malidp_regs.h
> > > b/drivers/gpu/drm/arm/malidp_regs.h
> > > index 993031542fa1..514c50dcb74d 100644
> > > --- a/drivers/gpu/drm/arm/malidp_regs.h
> > > +++ b/drivers/gpu/drm/arm/malidp_regs.h
> > > @@ -210,6 +210,16 @@
> > >  #define MALIDP500_CONFIG_VALID               0x00f00
> > >  #define MALIDP500_CONFIG_ID          0x00fd4
> > >
> > > +/*
> > > + * The quality of service (QoS) register on the DP500. RQOS register
> > > +values
> > > + * are driven by the ARQOS signal, using AXI transacations, dependent
> > > +on the
> > > + * FIFO input level.
> > > + * The RQOS register can also set QoS levels for:
> > > + *    - RED_ARQOS   @ A 4-bit signal value for close to underflow
> > conditions
> > > + *    - GREEN_ARQOS @ A 4-bit signal value for normal conditions
> > > + */
> > > +#define MALIDP500_RQOS_QUALITY          0x00500
> > > +
> > >  /* register offsets and bits specific to DP550/DP650 */
> > >  #define MALIDP550_ADDR_SPACE_SIZE    0x10000
> > >  #define MALIDP550_DE_CONTROL         0x00010
> > > --
> > > 2.17.1
> > >
> > 
> > --
> > ====================
> > | I would like to |
> > | fix the world,  |
> > | but they're not |
> > | giving me the   |
> >  \ source code!  /
> >   ---------------
> >     ¯\_(ツ)_/¯

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯

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