linux-kernel - Re: [PATCH] drm/ast: Atomic CR/SR reg R/W

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Message-ID: <7c128e03-842a-57b3-0c11-24fed9d4d126@suse.de>
Date:   Mon, 20 Sep 2021 10:17:11 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     KuoHsiang Chou <kuohsiang_chou@...eedtech.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     airlied@...hat.com, airlied@...ux.ie, daniel@...ll.ch,
        jenmin_yuan@...eedtech.com, arc_sung@...eedtech.com
Subject: Re: [PATCH] drm/ast: Atomic CR/SR reg R/W

Hi

Am 17.09.21 um 09:22 schrieb KuoHsiang Chou:
> 1. Avoid IO-index racing
> 2. IO-index racing happened on resolustion switching
>     and mouse moving at the same time
> 3. System hung while IO-index racing occurred.

I'd say that there's something else going one here. Mode setting and 
cursor movement should be protected against each other by DRM locking. 
Changing these low-level functions would not solve the issues. I'll try 
to reproduce the problem ASAP.

Best regards
Thomas

> 
> Signed-off-by: KuoHsiang Chou <kuohsiang_chou@...eedtech.com>
> ---
>   drivers/gpu/drm/ast/ast_main.c | 48 +++++++++++++++++++++++++---------
>   1 file changed, 36 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
> index 79a361867..1d8fa70c5 100644
> --- a/drivers/gpu/drm/ast/ast_main.c
> +++ b/drivers/gpu/drm/ast/ast_main.c
> @@ -41,28 +41,52 @@ void ast_set_index_reg_mask(struct ast_private *ast,
>   			    uint32_t base, uint8_t index,
>   			    uint8_t mask, uint8_t val)
>   {
> -	u8 tmp;
> -	ast_io_write8(ast, base, index);
> -	tmp = (ast_io_read8(ast, base + 1) & mask) | val;
> -	ast_set_index_reg(ast, base, index, tmp);
> +	uint16_t volatile usData;
> +	uint8_t  volatile jData;
> +
> +	do {
> +		ast_io_write8(ast, base, index);
> +		usData = ast_io_read16(ast, base);
> +	} while ((uint8_t)(usData) != index);
> +
> +	jData  = (uint8_t)(usData >> 8);
> +	jData &= mask;
> +	jData |= val;
> +	usData = ((uint16_t) jData << 8) | (uint16_t) index;
> +	ast_io_write16(ast, base, usData);
>   }
> 
>   uint8_t ast_get_index_reg(struct ast_private *ast,
>   			  uint32_t base, uint8_t index)
>   {
> -	uint8_t ret;
> -	ast_io_write8(ast, base, index);
> -	ret = ast_io_read8(ast, base + 1);
> -	return ret;
> +	uint16_t volatile usData;
> +	uint8_t  volatile jData;
> +
> +	do {
> +		ast_io_write8(ast, base, index);
> +		usData = ast_io_read16(ast, base);
> +	} while ((uint8_t)(usData) != index);
> +
> +	jData  = (uint8_t)(usData >> 8);
> +
> +	return jData;
>   }
> 
>   uint8_t ast_get_index_reg_mask(struct ast_private *ast,
>   			       uint32_t base, uint8_t index, uint8_t mask)
>   {
> -	uint8_t ret;
> -	ast_io_write8(ast, base, index);
> -	ret = ast_io_read8(ast, base + 1) & mask;
> -	return ret;
> +	uint16_t volatile usData;
> +	uint8_t  volatile jData;
> +
> +	do {
> +		ast_io_write8(ast, base, index);
> +		usData = ast_io_read16(ast, base);
> +	} while ((uint8_t)(usData) != index);
> +
> +	jData  = (uint8_t)(usData >> 8);
> +	jData &= mask;
> +
> +	return jData;
>   }
> 
>   static void ast_detect_config_mode(struct drm_device *dev, u32 *scu_rev)
> --
> 2.18.4
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer

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