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Date:   Fri, 11 Jan 2019 10:20:42 +0100
From:   Daniel Vetter <daniel@ffwll.ch>
To:     CK Hu <ck.hu@mediatek.com>,
        Noralf =?iso-8859-1?Q?Tr=F8nnes?= <noralf@tronnes.org>
Cc:     Daniel Vetter <daniel@ffwll.ch>,
        Frank Wunderlich <frank-w@public-files.de>,
        David Airlie <airlied@linux.ie>,
        Alexander Ryabchenko <d3adme4t@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: Re: [PATCH] drm/mediatek: Add MTK Framebuffer-Device (mt7623)
Message-ID: <20190111092042.GP21184@phenom.ffwll.local>
Mail-Followup-To: CK Hu <ck.hu@mediatek.com>,
        Noralf =?iso-8859-1?Q?Tr=F8nnes?= <noralf@tronnes.org>,
        Frank Wunderlich <frank-w@public-files.de>,
        David Airlie <airlied@linux.ie>,
        Alexander Ryabchenko <d3adme4t@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        "moderated list:ARM/Mediatek SoC support" <linux-mediatek@lists.infradead.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
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On Fri, Jan 11, 2019 at 11:20:09AM +0800, CK Hu wrote:
> Hi, Daniel:
> 
> On Thu, 2019-01-10 at 21:02 +0100, Daniel Vetter wrote:
> > On Thu, Jan 10, 2019 at 08:01:37PM +0100, Frank Wunderlich wrote:
> > > Hi Daniel,
> > > 
> > > > > Would be good to use the new generic fbdev emulation code here, for even
> > > > > less code. Or at least know why this isn't possible to use for mtk (and
> > > > > maybe address that in the core code). Hand-rolling fbdev code shouldn't be
> > > > > needed anymore.
> > > > 
> > > > Back on the mailing list, no private replies please:
> > > 
> > > i don't wanted to spam all people with dumb questions ;)
> > 
> > There's no dumb questions, only insufficient documentation :-)
> > 
> > > > For examples please grep for drm_fbdev_generic_setup(). There's also a
> > > > still in-flight series from Gerd Hoffmann to convert over bochs. That,
> > > > plus all the kerneldoc linked from there should get you started.
> > > > -Daniel
> > > 
> > > this is one of google best founds if i search for drm_fbdev_generic_setup:
> > > 
> > > https://lkml.org/lkml/2018/12/19/305
> > > 
> > > not very helpful...
> > > 
> > > so i tried kernel-doc
> > > 
> > > https://www.kernel.org/doc/html/latest/gpu/drm-kms-helpers.html?highlight=drm_fbdev_generic_setup#c.drm_fbdev_generic_setup
> > > 
> > > which is nice function-reference but i've found no generic workflow
> > > 
> > > as the posted driver is "only" a driver ported from kernel 4.4 by Alexander, i don't know if this new framework can be used and which parts need to be changed. I only try to bring his code Mainline....
> > > Maybe CK Hu can help here because driver is originally from him and he knows internals. Or maybe you can help here?
> > > 
> > > i personally make my first steps as spare-time kernel-developer :)
> > 
> > There's a ton of in-kernel users of that function already, I meant you can
> > use those to serve as examples ... If those + the kerneldoc aren't
> > good enough, then we need to improve them.
> > -Daniel
> 
> I've tried with drm_fbdev_generic_setup() and it works fine with simple
> modification. The patch is
> 
> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> @@ -16,6 +16,7 @@
>  #include <drm/drm_atomic.h>
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_crtc_helper.h>
> +#include <drm/drm_fb_helper.h>
>  #include <drm/drm_gem.h>
>  #include <drm/drm_gem_cma_helper.h>
>  #include <drm/drm_of.h>
> @@ -379,6 +380,7 @@ static void mtk_drm_kms_deinit(struct drm_device
> *drm)
>         .gem_prime_get_sg_table = mtk_gem_prime_get_sg_table,
>         .gem_prime_import_sg_table = mtk_gem_prime_import_sg_table,
>         .gem_prime_mmap = mtk_drm_gem_mmap_buf,
> +       .gem_prime_vmap = mtk_drm_gem_prime_vmap,
>         .ioctls = mtk_ioctls,
>         .num_ioctls = ARRAY_SIZE(mtk_ioctls),
>         .fops = &mtk_drm_fops,
> @@ -416,6 +418,8 @@ static int mtk_drm_bind(struct device *dev)
>         if (ret < 0)
>                 goto err_deinit;
> 
> +       drm_fbdev_generic_setup(drm, 32);
> +
>         return 0;
> 
> 
> But I implement .gem_prime_vmap with a workaround,
> 
> 
> --- a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> @@ -280,3 +280,8 @@ int mtk_gem_create_ioctl(struct drm_device *dev,
> void *data,
>         mtk_drm_gem_free_object(&mtk_gem->base);
>         return ret;
>  }
> +
> +void *mtk_drm_gem_prime_vmap(struct drm_gem_object *obj)
> +{
> +       return (void *)1;
> +}
> 
> Current drm_fb_helper depends on drm_client to create fbdev. When
> drm_client create drm_client_buffer, it need to vmap to get kernel
> vaddr. But I think for fbdev, the vaddr is useless. Do you agree that I
> temporarily implement .gem_prime_vmap in such way?

The vmap is used by fbcon, without that fbdev won't really work I think.
So I'm rather confused on what you tested ...

Adding Noralf, he's the expert here.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch