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From:   Thomas Zimmermann <tzimmermann@suse.de>
To:     Tian Tao <tiantao6@hisilicon.com>,
        maarten.lankhorst@linux.intel.com, mripard@kernel.org,
        airlied@linux.ie, daniel@ffwll.ch, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
References: <1604315990-56787-1-git-send-email-tiantao6@hisilicon.com>
 <8a76d144-f8ba-bbbc-9177-53088f6dc73a@suse.de>
Subject: Re: [PATCH] drm/irq: Add irq as false detection
Message-ID: <d0b8c494-0d08-11ae-c0e9-988dbf9ecd35@suse.de>
Date:   Mon, 2 Nov 2020 13:40:15 +0100
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From: Thomas Zimmermann <tzimmermann@suse.de>
To: Tian Tao <tiantao6@hisilicon.com>, maarten.lankhorst@linux.intel.com,
 mripard@kernel.org, airlied@linux.ie, daniel@ffwll.ch,
 dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Message-ID: <d0b8c494-0d08-11ae-c0e9-988dbf9ecd35@suse.de>
Subject: Re: [PATCH] drm/irq: Add irq as false detection
References: <1604315990-56787-1-git-send-email-tiantao6@hisilicon.com>
 <8a76d144-f8ba-bbbc-9177-53088f6dc73a@suse.de>
In-Reply-To: <8a76d144-f8ba-bbbc-9177-53088f6dc73a@suse.de>

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Hi

Am 02.11.20 um 13:09 schrieb Thomas Zimmermann:
> Hi
>=20
> Am 02.11.20 um 12:19 schrieb Tian Tao:
>> Add the detection of false for irq, so that the EINVAL is not
>> returned when dev->irq_enabled is false.
>>
>> Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
>> ---
>>  drivers/gpu/drm/drm_irq.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
>> index 09d6e9e..7537a3d 100644
>> --- a/drivers/gpu/drm/drm_irq.c
>> +++ b/drivers/gpu/drm/drm_irq.c
>> @@ -172,6 +172,9 @@ int drm_irq_uninstall(struct drm_device *dev)
>>  	bool irq_enabled;
>>  	int i;
>> =20
>> +	if (!dev->irq_enabled || !dev)
>> +		return 0;
>> +
>=20
> Dereferencing a pointer before NULL-checking it, is Yoda programming. :=
)
> I'd just drop the test for !dev and assume that dev is always valid.
>=20
> I suggest to change the int return value to void and return nothing.
>=20
> Re-reading the actual implementation of this function, this location
> might be too early. Further below there already is a test for
> irq_enabled. Put a drm_WARN_ON around it and it should be fine. This wa=
y
> the vblank handlers will be disabled and erroneous callers will see a
> warning in the kernel's log.

In addition to these changes, you could also add a managed
implementation of drm_irq_install(). The canonical name should be
devm_drm_irq_install(). The function would call drm_irq_install() and
register a cleanup handler via devm_add_action(). Example code is at [1].=


KMS drivers, such as hibmc, would then not have to bother about
uninstalling the DRM irq.

Best regards
Thomas

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/d=
rivers/gpu/drm/drm_drv.c#n664


>=20
> Best regards
> Thomas
>=20
>>  	irq_enabled =3D dev->irq_enabled;
>>  	dev->irq_enabled =3D false;
>> =20
>>
>=20
>=20
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel
>=20

--=20
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 N=C3=BCrnberg, Germany
(HRB 36809, AG N=C3=BCrnberg)
Gesch=C3=A4ftsf=C3=BChrer: Felix Imend=C3=B6rffer

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