Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 18 Jul 2019 14:17:37 +0100
From:   Liviu Dudau <Liviu.Dudau@arm.com>
To:     "Lowry Li (Arm Technology China)" <Lowry.Li@arm.com>
Cc:     "james qian wang (Arm Technology China)" <james.qian.wang@arm.com>,
        "maarten.lankhorst@linux.intel.com" 
        <maarten.lankhorst@linux.intel.com>,
        "seanpaul@chromium.org" <seanpaul@chromium.org>,
        "airlied@linux.ie" <airlied@linux.ie>,
        Brian Starkey <Brian.Starkey@arm.com>,
        "Julien Yin (Arm Technology China)" <Julien.Yin@arm.com>,
        "Jonathan Chai (Arm Technology China)" <Jonathan.Chai@arm.com>,
        Ayan Halder <Ayan.Halder@arm.com>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        nd <nd@arm.com>
Subject: Re: [PATCH] drm/komeda: Adds error event print functionality
Message-ID: <20190718131737.GD5942@e110455-lin.cambridge.arm.com>
References: <1561604994-26925-1-git-send-email-lowry.li@arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
Content-Transfer-Encoding: 8bit
In-Reply-To: <1561604994-26925-1-git-send-email-lowry.li@arm.com>
User-Agent: Mutt/1.12.1 (2019-06-15)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Jun 27, 2019 at 04:10:36AM +0100, Lowry Li (Arm Technology China) wrote:
> Adds to print the event message when error happens and the same event
> will not be printed until next vsync.
> 
> Signed-off-by: Lowry Li (Arm Technology China) <lowry.li@arm.com>
> ---
>  drivers/gpu/drm/arm/display/komeda/Makefile       |   1 +
>  drivers/gpu/drm/arm/display/komeda/komeda_dev.h   |  13 ++
>  drivers/gpu/drm/arm/display/komeda/komeda_event.c | 144 ++++++++++++++++++++++
>  drivers/gpu/drm/arm/display/komeda/komeda_kms.c   |   2 +
>  4 files changed, 160 insertions(+)
>  create mode 100644 drivers/gpu/drm/arm/display/komeda/komeda_event.c
> 
> diff --git a/drivers/gpu/drm/arm/display/komeda/Makefile b/drivers/gpu/drm/arm/display/komeda/Makefile
> index 38aa584..3f53d2d 100644
> --- a/drivers/gpu/drm/arm/display/komeda/Makefile
> +++ b/drivers/gpu/drm/arm/display/komeda/Makefile
> @@ -7,6 +7,7 @@ ccflags-y := \
>  komeda-y := \
>  	komeda_drv.o \
>  	komeda_dev.o \
> +	komeda_event.o \
>  	komeda_format_caps.o \
>  	komeda_coeffs.o \
>  	komeda_color_mgmt.o \
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_dev.h b/drivers/gpu/drm/arm/display/komeda/komeda_dev.h
> index 096f9f7..e863ec3 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_dev.h
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_dev.h
> @@ -40,6 +40,17 @@
>  #define KOMEDA_ERR_TTNG			BIT_ULL(30)
>  #define KOMEDA_ERR_TTF			BIT_ULL(31)
>  
> +#define KOMEDA_ERR_EVENTS	\
> +	(KOMEDA_EVENT_URUN	| KOMEDA_EVENT_IBSY	| KOMEDA_EVENT_OVR |\
> +	KOMEDA_ERR_TETO		| KOMEDA_ERR_TEMR	| KOMEDA_ERR_TITR |\
> +	KOMEDA_ERR_CPE		| KOMEDA_ERR_CFGE	| KOMEDA_ERR_AXIE |\
> +	KOMEDA_ERR_ACE0		| KOMEDA_ERR_ACE1	| KOMEDA_ERR_ACE2 |\
> +	KOMEDA_ERR_ACE3		| KOMEDA_ERR_DRIFTTO	| KOMEDA_ERR_FRAMETO |\
> +	KOMEDA_ERR_ZME		| KOMEDA_ERR_MERR	| KOMEDA_ERR_TCF |\
> +	KOMEDA_ERR_TTNG		| KOMEDA_ERR_TTF)
> +
> +#define KOMEDA_WARN_EVENTS	KOMEDA_ERR_CSCE
> +
>  /* malidp device id */
>  enum {
>  	MALI_D71 = 0,
> @@ -207,6 +218,8 @@ struct komeda_dev {
>  
>  struct komeda_dev *dev_to_mdev(struct device *dev);
>  
> +void komeda_print_events(struct komeda_events *evts);
> +
>  int komeda_dev_resume(struct komeda_dev *mdev);
>  int komeda_dev_suspend(struct komeda_dev *mdev);
>  #endif /*_KOMEDA_DEV_H_*/
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_event.c b/drivers/gpu/drm/arm/display/komeda/komeda_event.c
> new file mode 100644
> index 0000000..309dbe2
> --- /dev/null
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_event.c
> @@ -0,0 +1,144 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * (C) COPYRIGHT 2019 ARM Limited. All rights reserved.
> + * Author: James.Qian.Wang <james.qian.wang@arm.com>
> + *
> + */
> +#include <drm/drm_print.h>
> +
> +#include "komeda_dev.h"
> +
> +struct komeda_str {
> +	char *str;
> +	u32 sz;
> +	u32 len;
> +};
> +
> +/* return 0 on success,  < 0 on no space.
> + */
> +static int komeda_sprintf(struct komeda_str *str, const char *fmt, ...)
> +{
> +	va_list args;
> +	int num, free_sz;
> +	int err;
> +
> +	free_sz = str->sz - str->len;
> +	if (free_sz <= 0)
> +		return -ENOSPC;
> +
> +	va_start(args, fmt);
> +
> +	num = vsnprintf(str->str + str->len, free_sz, fmt, args);
> +
> +	va_end(args);
> +
> +	if (num <= free_sz) {
> +		str->len += num;
> +		err = 0;
> +	} else {
> +		str->len = str->sz;
> +		err = -ENOSPC;
> +	}
> +
> +	return err;
> +}
> +
> +static void evt_sprintf(struct komeda_str *str, u64 evt, const char *msg)
> +{
> +	if (evt)
> +		komeda_sprintf(str, msg);
> +}

Why do we need this wrapper?

> +
> +static void evt_str(struct komeda_str *str, u64 events)
> +{
> +	if (events == 0ULL) {
> +		evt_sprintf(str, 1, "None");
> +		return;
> +	}
> +
> +	evt_sprintf(str, events & KOMEDA_EVENT_VSYNC, "VSYNC|");
> +	evt_sprintf(str, events & KOMEDA_EVENT_FLIP, "FLIP|");
> +	evt_sprintf(str, events & KOMEDA_EVENT_EOW, "EOW|");
> +	evt_sprintf(str, events & KOMEDA_EVENT_MODE, "OP-MODE|");
> +
> +	evt_sprintf(str, events & KOMEDA_EVENT_URUN, "UNDERRUN|");
> +	evt_sprintf(str, events & KOMEDA_EVENT_OVR, "OVERRUN|");
> +
> +	/* GLB error */
> +	evt_sprintf(str, events & KOMEDA_ERR_MERR, "MERR|");
> +	evt_sprintf(str, events & KOMEDA_ERR_FRAMETO, "FRAMETO|");
> +
> +	/* DOU error */
> +	evt_sprintf(str, events & KOMEDA_ERR_DRIFTTO, "DRIFTTO|");
> +	evt_sprintf(str, events & KOMEDA_ERR_FRAMETO, "FRAMETO|");
> +	evt_sprintf(str, events & KOMEDA_ERR_TETO, "TETO|");
> +	evt_sprintf(str, events & KOMEDA_ERR_CSCE, "CSCE|");
> +
> +	/* LPU errors or events */
> +	evt_sprintf(str, events & KOMEDA_EVENT_IBSY, "IBSY|");
> +	evt_sprintf(str, events & KOMEDA_ERR_AXIE, "AXIE|");
> +	evt_sprintf(str, events & KOMEDA_ERR_ACE0, "ACE0|");
> +	evt_sprintf(str, events & KOMEDA_ERR_ACE1, "ACE1|");
> +	evt_sprintf(str, events & KOMEDA_ERR_ACE2, "ACE2|");
> +	evt_sprintf(str, events & KOMEDA_ERR_ACE3, "ACE3|");
> +
> +	/* LPU TBU errors*/
> +	evt_sprintf(str, events & KOMEDA_ERR_TCF, "TCF|");
> +	evt_sprintf(str, events & KOMEDA_ERR_TTNG, "TTNG|");
> +	evt_sprintf(str, events & KOMEDA_ERR_TITR, "TITR|");
> +	evt_sprintf(str, events & KOMEDA_ERR_TEMR, "TEMR|");
> +	evt_sprintf(str, events & KOMEDA_ERR_TTF, "TTF|");
> +
> +	/* CU errors*/
> +	evt_sprintf(str, events & KOMEDA_ERR_CPE, "COPROC|");
> +	evt_sprintf(str, events & KOMEDA_ERR_ZME, "ZME|");
> +	evt_sprintf(str, events & KOMEDA_ERR_CFGE, "CFGE|");
> +	evt_sprintf(str, events & KOMEDA_ERR_TEMR, "TEMR|");
> +
> +	if (str->len > 0 && (str->str[str->len - 1] == '|')) {
> +		str->str[str->len - 1] = 0;
> +		str->len--;
> +	}
> +}
> +
> +static bool is_new_frame(struct komeda_events *a)
> +{
> +	return (a->pipes[0] | a->pipes[1]) & KOMEDA_EVENT_FLIP;
> +}
> +
> +void komeda_print_events(struct komeda_events *evts)
> +{
> +	u64 print_evts = KOMEDA_ERR_EVENTS;
> +	static bool en_print = true;
> +
> +	/* reduce the same msg print, only print the first evt for one frame */
> +	if (evts->global || is_new_frame(evts))
> +		en_print = true;
> +	if (!en_print)
> +		return;

When does en_print ever get false?

> +
> +#ifdef DEBUG
> +	print_evts |= KOMEDA_WARN_EVENTS;
> +#endif
> +
> +	if ((evts->global | evts->pipes[0] | evts->pipes[1]) & print_evts) {
> +		#define STR_SZ		128
> +		char msg[STR_SZ];

I've counted about 27 evt_sprintf() calls in evt_str() function, with an
average of 5 characters each, so thats 135 characters printed into a buffer
that is only 128 bytes. Please don't do this!

> +		struct komeda_str str;
> +
> +		str.str = msg;
> +		str.sz  = STR_SZ;
> +		str.len = 0;
> +
> +		komeda_sprintf(&str, "gcu: ");
> +		evt_str(&str, evts->global);
> +		komeda_sprintf(&str, ", pipes[0]: ");
> +		evt_str(&str, evts->pipes[0]);
> +		komeda_sprintf(&str, ", pipes[1]: ");
> +		evt_str(&str, evts->pipes[1]);
> +
> +		DRM_ERROR("err detect: %s\n", msg);
> +
> +		en_print = false;
> +	}
> +}
> diff --git a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> index 647bce5..1462bac 100644
> --- a/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> +++ b/drivers/gpu/drm/arm/display/komeda/komeda_kms.c
> @@ -47,6 +47,8 @@ static irqreturn_t komeda_kms_irq_handler(int irq, void *data)
>  	memset(&evts, 0, sizeof(evts));
>  	status = mdev->funcs->irq_handler(mdev, &evts);
>  
> +	komeda_print_events(&evts);

Calling this function from the IRQ handler is a bad idea. We should use debugfs
if you really want to have a trace of the events, but I personally don't see
value in having this functionality in the kernel at all. You can expose the
value of the evts->global and evts->pipes[] as integers and decode that in
userspace or as a debugfs entry.

Best regards,
Liviu

> +
>  	/* Notify the crtc to handle the events */
>  	for (i = 0; i < kms->n_crtcs; i++)
>  		komeda_crtc_handle_event(&kms->crtcs[i], &evts);
> -- 
> 1.9.1
> 

-- 
====================
| I would like to |
| fix the world,  |
| but they're not |
| giving me the   |
 \ source code!  /
  ---------------
    ¯\_(ツ)_/¯