Date:   Wed, 22 Jan 2020 07:43:34 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Sean Paul <sean@...rly.run>
Cc:     Douglas Anderson <dianders@...omium.org>,
        saiprakash.ranjan@...eaurora.org,
        Matthias Kaehlcke <mka@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Sean Paul <seanpaul@...omium.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        David Airlie <airlied@...ux.ie>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [REPOST PATCH] drm/msm: Set dma maximum segment size for mdss

On Wed, Jan 22, 2020 at 6:51 AM Sean Paul <sean@...rly.run> wrote:
>
> On Tue, Jan 21, 2020 at 11:26:05AM -0800, Rob Clark wrote:
> > On Tue, Jan 21, 2020 at 11:19 AM Douglas Anderson <dianders@...omium.org> wrote:
> > >
> > > From: Sean Paul <seanpaul@...omium.org>
> > >
> > > Turning on CONFIG_DMA_API_DEBUG_SG results in the following error:
> > >
> > > [   12.078665] msm ae00000.mdss: DMA-API: mapping sg segment longer than device claims to support [len=3526656] [max=65536]
> > > [   12.089870] WARNING: CPU: 6 PID: 334 at /mnt/host/source/src/third_party/kernel/v4.19/kernel/dma/debug.c:1301 debug_dma_map_sg+0x1dc/0x318
> > > [   12.102655] Modules linked in: joydev
> > > [   12.106442] CPU: 6 PID: 334 Comm: frecon Not tainted 4.19.0 #2
> > > [   12.112450] Hardware name: Google Cheza (rev3+) (DT)
> > > [   12.117566] pstate: 60400009 (nZCv daif +PAN -UAO)
> > > [   12.122506] pc : debug_dma_map_sg+0x1dc/0x318
> > > [   12.126995] lr : debug_dma_map_sg+0x1dc/0x318
> > > [   12.131487] sp : ffffff800cc3ba80
> > > [   12.134913] x29: ffffff800cc3ba80 x28: 0000000000000000
> > > [   12.140395] x27: 0000000000000004 x26: 0000000000000004
> > > [   12.145868] x25: ffffff8008e55b18 x24: 0000000000000000
> > > [   12.151337] x23: 00000000ffffffff x22: ffffff800921c000
> > > [   12.156809] x21: ffffffc0fa75b080 x20: ffffffc0f7195090
> > > [   12.162280] x19: ffffffc0f1c53280 x18: 0000000000000000
> > > [   12.167749] x17: 0000000000000000 x16: 0000000000000000
> > > [   12.173218] x15: 0000000000000000 x14: 0720072007200720
> > > [   12.178689] x13: 0720072007200720 x12: 0720072007200720
> > > [   12.184161] x11: 0720072007200720 x10: 0720072007200720
> > > [   12.189641] x9 : ffffffc0f1fc6b60 x8 : 0000000000000000
> > > [   12.195110] x7 : ffffff8008132ce0 x6 : 0000000000000000
> > > [   12.200585] x5 : 0000000000000000 x4 : ffffff8008134734
> > > [   12.206058] x3 : ffffff800cc3b830 x2 : ffffffc0f1fc6240
> > > [   12.211532] x1 : 25045a74f48a7400 x0 : 25045a74f48a7400
> > > [   12.217006] Call trace:
> > > [   12.219535]  debug_dma_map_sg+0x1dc/0x318
> > > [   12.223671]  get_pages+0x19c/0x20c
> > > [   12.227177]  msm_gem_fault+0x64/0xfc
> > > [   12.230874]  __do_fault+0x3c/0x140
> > > [   12.234383]  __handle_mm_fault+0x70c/0xdb8
> > > [   12.238603]  handle_mm_fault+0xac/0xc4
> > > [   12.242473]  do_page_fault+0x1bc/0x3d4
> > > [   12.246342]  do_translation_fault+0x54/0x88
> > > [   12.250652]  do_mem_abort+0x60/0xf0
> > > [   12.254250]  el0_da+0x20/0x24
> > > [   12.257317] irq event stamp: 67260
> > > [   12.260828] hardirqs last  enabled at (67259): [<ffffff8008132d0c>] console_unlock+0x214/0x608
> > > [   12.269693] hardirqs last disabled at (67260): [<ffffff8008080e0c>] do_debug_exception+0x5c/0x178
> > > [   12.278820] softirqs last  enabled at (67256): [<ffffff8008081664>] __do_softirq+0x4d4/0x520
> > > [   12.287510] softirqs last disabled at (67249): [<ffffff80080be574>] irq_exit+0xa8/0x100
> > > [   12.295742] ---[ end trace e63cfc40c313ffab ]---
> > >
> > > The root of the problem is that the default segment size for sgt is
> > > (UINT_MAX & PAGE_MASK), and the default segment size for device dma is
> > > 64K. As such, if you compare the 2, you would deduce that the sg segment
> > > will overflow the device's capacity. In reality, the hardware can
> > > accommodate the larger sg segments, it's just not initializing its max
> > > segment properly. This patch initializes the max segment size for the
> > > mdss device, which gets rid of that pesky warning.
> > >
> > > Reported-by: Stephen Boyd <swboyd@...omium.org>
> > > Signed-off-by: Sean Paul <seanpaul@...omium.org>
> > > Tested-by: Stephen Boyd <swboyd@...omium.org>
> > > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > > ---
> > > This patch has been floating in the ether for over a year [1].  I know
> > > next to nothing about it, but I'm told it's still useful so I'm
> > > helpfully reposting it.  Please enjoy.
> >
> > This looks like the right thing to do.. sorry I overlooked the patch
> > first time around
> >
> > Reviewed-by: Rob Clark <robdclark@...il.com>
> >
> > (since I've already sent PR for msm-next, could we pick this up via drm-misc?)
>
> You got it, pushed to drm-misc-next-fixes.
>

thx

BR,
-R

> Thanks
>
> Sean
>
> >
> > BR,
> > -R
> >
> >
> > >
> > > [1] https://lore.kernel.org/r/20181106213239.52133-1-sean@poorly.run
> > >
> > >  drivers/gpu/drm/msm/msm_drv.c | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> > > index c26219c7a49f..e4b750b0c2d3 100644
> > > --- a/drivers/gpu/drm/msm/msm_drv.c
> > > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > > @@ -441,6 +441,14 @@ static int msm_drm_init(struct device *dev, struct drm_driver *drv)
> > >         if (ret)
> > >                 goto err_msm_uninit;
> > >
> > > +       if (!dev->dma_parms) {
> > > +               dev->dma_parms = devm_kzalloc(dev, sizeof(*dev->dma_parms),
> > > +                                             GFP_KERNEL);
> > > +               if (!dev->dma_parms)
> > > +                       return -ENOMEM;
> > > +       }
> > > +       dma_set_max_seg_size(dev, DMA_BIT_MASK(32));
> > > +
> > >         msm_gem_shrinker_init(ddev);
> > >
> > >         switch (get_mdp_ver(pdev)) {
> > > --
> > > 2.25.0.341.g760bfbb309-goog
> > >
>
> --
> Sean Paul, Software Engineer, Google / Chromium OS

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