linux-kernel - Re: [PATCH v7 4/7] drm/log: Do not draw if drm

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Message-ID: <5e19d9d4-7533-4a59-a665-cfc4a8195293@suse.de>
Date: Fri, 8 Nov 2024 14:33:06 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Jocelyn Falempe <jfalempe@...hat.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>, John Ogness <john.ogness@...utronix.de>,
 Javier Martinez Canillas <javierm@...hat.com>,
 "Guilherme G . Piccoli" <gpiccoli@...lia.com>,
 bluescreen_avenger@...izon.net, Caleb Connolly <caleb.connolly@...aro.org>,
 Petr Mladek <pmladek@...e.com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 4/7] drm/log: Do not draw if drm_master is taken

Hi

Am 08.11.24 um 09:10 schrieb Jocelyn Falempe:
> When userspace takes drm_master, the drm_client buffer is no more
> visible, so drm_log shouldn't waste CPU cycle to draw on it.
>
> Signed-off-by: Jocelyn Falempe <jfalempe@...hat.com>
> ---
>   drivers/gpu/drm/drm_log.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_log.c b/drivers/gpu/drm/drm_log.c
> index 376ee173d99d9..226e206e8b6a3 100644
> --- a/drivers/gpu/drm/drm_log.c
> +++ b/drivers/gpu/drm/drm_log.c
> @@ -18,6 +18,7 @@
>   #include <drm/drm_print.h>
>   
>   #include "drm_draw.h"
> +#include "drm_internal.h"
>   #include "drm_log.h"
>   
>   MODULE_AUTHOR("Jocelyn Falempe");
> @@ -308,8 +309,13 @@ static void drm_log_write_thread(struct console *con, struct nbcon_write_context
>   	if (!dlog->probed)
>   		drm_log_init_client(dlog);
>   
> -	for (i = 0; i < dlog->n_scanout; i++)
> -		drm_log_draw_kmsg_record(&dlog->scanout[i], wctxt->outbuf, wctxt->len);
> +	/* Check that we are still the master before drawing */
> +	if (drm_master_internal_acquire(dlog->client.dev)) {

Just a note: it would be better to track this state in the client code 
and handle these locks automatically. But it's ok for now. It would 
require an overhaul of the fbdev helpers as well.

> +		drm_master_internal_release(dlog->client.dev);

Don't you have to release after drawing?

Best regards
Thomas

> +
> +		for (i = 0; i < dlog->n_scanout; i++)
> +			drm_log_draw_kmsg_record(&dlog->scanout[i], wctxt->outbuf, wctxt->len);
> +	}
>   }
>   
>   static void drm_log_lock(struct console *con, unsigned long *flags)

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)