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Message-ID: <96aded2c-f083-6e3d-c07d-f392f52a01b0@ideasonboard.com>
Date: Thu, 19 Sep 2019 09:08:18 +0100
From: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Jacopo Mondi <jacopo@...ndi.org>,
Jacopo Mondi <jacopo+renesas@...ndi.org>, geert@...ux-m68k.org,
horms@...ge.net.au, uli+renesas@...nd.eu,
VenkataRajesh.Kalakodima@...bosch.com, airlied@...ux.ie,
daniel@...ll.ch, koji.matsuoka.xm@...esas.com, muroya@....co.jp,
Harsha.ManjulaMallikarjun@...bosch.com,
linux-renesas-soc@...r.kernel.org, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 6/9] drm: rcar-du: crtc: Enable and disable CMMs
Hi Laurent, / Jacopo
On 19/09/2019 00:23, Laurent Pinchart wrote:
> Hello,
>
> On Thu, Sep 12, 2019 at 10:19:30AM +0100, Kieran Bingham wrote:
>> On 12/09/2019 09:07, Jacopo Mondi wrote:
>>> On Wed, Sep 11, 2019 at 07:40:27PM +0100, Kieran Bingham wrote:
>>>> On 06/09/2019 14:54, Jacopo Mondi wrote:
>>>>> Enable/disable the CMM associated with a CRTC at CRTC start and stop
>>>>> time and enable the CMM unit through the Display Extensional Functions
>>>>> register at group setup time.
>>>>>
>>>>> Reviewed-by: Ulrich Hecht <uli+renesas@...nd.eu>
>>>>> Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>>>>> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.org>
>>>>> ---
>>>>> drivers/gpu/drm/rcar-du/rcar_du_crtc.c | 7 +++++++
>>>>> drivers/gpu/drm/rcar-du/rcar_du_group.c | 8 ++++++++
>>>>> drivers/gpu/drm/rcar-du/rcar_du_regs.h | 5 +++++
>>>>> 3 files changed, 20 insertions(+)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
>>>>> index 23f1d6cc1719..3dac605c3a67 100644
>>>>> --- a/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
>>>>> +++ b/drivers/gpu/drm/rcar-du/rcar_du_crtc.c
>>>>> @@ -21,6 +21,7 @@
>>>>> #include <drm/drm_plane_helper.h>
>>>>> #include <drm/drm_vblank.h>
>>>>>
>>>>> +#include "rcar_cmm.h"
>>>>> #include "rcar_du_crtc.h"
>>>>> #include "rcar_du_drv.h"
>>>>> #include "rcar_du_encoder.h"
>>>>> @@ -619,6 +620,9 @@ static void rcar_du_crtc_stop(struct rcar_du_crtc *rcrtc)
>>>>> if (rcar_du_has(rcrtc->dev, RCAR_DU_FEATURE_VSP1_SOURCE))
>>>>> rcar_du_vsp_disable(rcrtc);
>>>>>
>>>>> + if (rcrtc->cmm)
>>>>> + rcar_cmm_disable(rcrtc->cmm);
>>>>> +
>>>>> /*
>>>>> * Select switch sync mode. This stops display operation and configures
>>>>> * the HSYNC and VSYNC signals as inputs.
>>>>> @@ -686,6 +690,9 @@ static void rcar_du_crtc_atomic_enable(struct drm_crtc *crtc,
>>>>> }
>>>>>
>>>>> rcar_du_crtc_start(rcrtc);
>>>>> +
>>>>> + if (rcrtc->cmm)
>>>>> + rcar_cmm_enable(rcrtc->cmm);
>>>>> }
>>>>>
>>>>> static void rcar_du_crtc_atomic_disable(struct drm_crtc *crtc,
>>>>> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_group.c b/drivers/gpu/drm/rcar-du/rcar_du_group.c
>>>>> index 9eee47969e77..25d0fc125d7a 100644
>>>>> --- a/drivers/gpu/drm/rcar-du/rcar_du_group.c
>>>>> +++ b/drivers/gpu/drm/rcar-du/rcar_du_group.c
>>>>> @@ -147,6 +147,14 @@ static void rcar_du_group_setup(struct rcar_du_group *rgrp)
>>>>>
>>>>> rcar_du_group_setup_pins(rgrp);
>>>>>
>>>>> + if (rcar_du_has(rcdu, RCAR_DU_FEATURE_CMM)) {
>>>>> + u32 defr7 = DEFR7_CODE
>>>>> + | (rgrp->cmms_mask & BIT(1) ? DEFR7_CMME1 : 0)
>>>>> + | (rgrp->cmms_mask & BIT(0) ? DEFR7_CMME0 : 0);
>>>>> +
>>>>> + rcar_du_group_write(rgrp, DEFR7, defr7);
>>>>> + }
>>>>> +
>>>>
>>>> What's the effect here on platforms with a CMM, but with
>>>> CONFIG_DRM_RCAR_CMM unset?
>>>>
>>>> Will this incorrectly configure the DU ?
>>>>
>>>> Will it stall the display if the DU tries to interact with another
>>>> module which is not enabled?
>>>
>>> I recall I tested that (that's why I had to add stubs for CMM
>>> functions, as I had linkage errors otherwise) and thing seems to be
>>> fine as the CMM configuration/enblement resolve to an empty function.
>>
>> Yes, I see the stubs to allow for linkage, but it's the hardware I'm
>> concerned about. If it passes the tests and doesn't break then that's
>> probably ok ... but I'm really weary that we're enabling a hardware
>> pipeline with a disabled component in the middle.
>>
>>> Would you prefer to have this guarded by an #if IS_ENABLED() ?
>>
>> I don't think we need a compile time conditional, but I'd say it
>> probably needs to be more about whether the CMM has actually probed or not
>>
>> Aha, and I see that in rcar_du_cmm_init() we already do a
>> call to rcar_cmm_init(), which if fails will leave rcdu->cmms[i] as
>> NULL. So that's catered for, which results in the rgrp->cmms_mask being
>> correctly representative of whether there is a CMM connected or not.
>
> Doesn't this result in probe failure ?
I think I mis-spoke above, I didn't mean "if rcar_cmm_init() fails" I
meant "if rcar_du_cmm_init() determines there are no connected CMM's or
if they are disabled."
If rcar_cmm_init() returns a failure, then yes we will fail to probe.
But I think it's up to rcar_du_cmm_init() to determine if the CMM exists
or not (or is enabled) and if that's not a failure case then it should
not prevent the probing of the DU.
In fact, I've now seen that if CONFIG_DRM_RCAR_CMM is not enabled,
rcar_cmm_init() returns 0, and I think in fact it should return -ENODEV,
with an exception on that return value in rcar_du_cmm_init() so that the
DU continues with no CMM attached there.
>
>> ... so I think that means the ...
>> "if (rcar_du_has(rcdu, RCAR_DU_FEATURE_CMM))" is somewhat redundant:
>>
>>
>> This could be:
>>
>> if (rgrp->cmms_mask) {
>> u32 defr7 = DEFR7_CODE
>> | (rgrp->cmms_mask & BIT(1) ? DEFR7_CMME1 : 0)
>> | (rgrp->cmms_mask & BIT(0) ? DEFR7_CMME0 : 0);
>>
>> rcar_du_group_write(rgrp, DEFR7, defr7);
>>
>> Or in fact, if we don't mind writing 0 to DEFR7 when there is no CMM
>> (which is safe by the looks of things as DEFR7 is available on all
>> platforms), then we can even remove the outer conditional, and leave
>> this all up to the ternary operators to write the correct value to the
>> defr7.
>>
>> Phew ... net result - your current code *is* safe with the
>> CONFIG_DRM_RCAR_CMM option disabled. I'll leave it up to you if you want
>> to simplify the code here and remove the RCAR_DU_FEATURE_CMM.
>>
>> As this RCAR_DU_FEATURE_CMM flag is only checked here, removing it would
>> however simplify all of the rcar_du_device_info structures.
>>
>> So - with or without the _FEATURE_CMM" simplification, this patch looks
>> functional and safe so:
>>
>>
>> Reviewed-by: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
>>
>>>>> if (rcdu->info->gen >= 2) {
>>>>> rcar_du_group_setup_defr8(rgrp);
>>>>> rcar_du_group_setup_didsr(rgrp);
>>>>> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_regs.h b/drivers/gpu/drm/rcar-du/rcar_du_regs.h
>>>>> index bc87f080b170..fb9964949368 100644
>>>>> --- a/drivers/gpu/drm/rcar-du/rcar_du_regs.h
>>>>> +++ b/drivers/gpu/drm/rcar-du/rcar_du_regs.h
>>>>> @@ -197,6 +197,11 @@
>>>>> #define DEFR6_MLOS1 (1 << 2)
>>>>> #define DEFR6_DEFAULT (DEFR6_CODE | DEFR6_TCNE1)
>>>>>
>>>>> +#define DEFR7 0x000ec
>>>>> +#define DEFR7_CODE (0x7779 << 16)
>>>>> +#define DEFR7_CMME1 BIT(6)
>>>>> +#define DEFR7_CMME0 BIT(4)
>>>>> +
>>>>> /* -----------------------------------------------------------------------------
>>>>> * R8A7790-only Control Registers
>>>>> */
>
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