linux-kernel - Re: [PATCH v8 1/3] media: rcar-csi2: Correct the selection of hsfreqrange

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Date:   Wed, 1 Jul 2020 00:03:53 +0200
From:   Niklas Söderlund 
        <niklas.soderlund@...natech.se>
To:     Suresh Udipi <sudipi@...adit-jv.com>
Cc:     mrodin@...adit-jv.com, akiyama@...-osk.co.jp,
        efriedrich@...adit-jv.com, erosca@...adit-jv.com,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-renesas-soc@...r.kernel.org, mchehab@...nel.org,
        michael@...in.online, securitycheck@...so.co.jp
Subject: Re: [PATCH v8 1/3] media: rcar-csi2: Correct the selection of
 hsfreqrange

Hi Suresh,

Thanks for your work.

On 2020-06-18 19:34:30 +0900, Suresh Udipi wrote:
> hsfreqrange should be chosen based on the calculated mbps which
> is closer to the default bit rate  and within the range as per
> table[1]. But current calculation always selects first value which
> is greater than or equal to the calculated mbps which may lead
> to chosing a wrong range in some cases.
> 
> For example for 360 mbps for H3/M3N
> Existing logic selects
> Calculated value 360Mbps : Default 400Mbps Range [368.125 -433.125 mbps]
> 
> This hsfreqrange is out of range.
> 
> The logic is changed to get the default value which is closest to the
> calculated value [1]
> 
> Calculated value 360Mbps : Default 350Mbps  Range [320.625 -380.625 mpbs]
> 
> [1] specs r19uh0105ej0200-r-car-3rd-generation.pdf [Table 25.9]
> 
> Please note that According to Renesas in Table 25.9 the range for
> 220 default value is corrected as below
> 
>  |Range (Mbps)     |  Default  Bit rate (Mbps) |
>  -----------------------------------------------
>  | 197.125-244.125 |     220                   |
>  -----------------------------------------------
> 
> Fixes: 769afd212b16 ("media: rcar-csi2: add Renesas R-Car MIPI CSI-2 receiver driver")
> 
> Signed-off-by: Suresh Udipi <sudipi@...adit-jv.com>
> Signed-off-by: Kazuyoshi Akiyama <akiyama@...-osk.co.jp>
> Signed-off-by: Michael Rodin <mrodin@...adit-jv.com>

Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>

> ---
>  Changes in v2:
>   - Added the boundary check for the maximum bit rate.
> 
>   - Simplified the logic by remmoving range check
>     as only the closest default value covers most
>     of the use cases.
> 
>   - Aligning the commit message based on the above change
> 
> 
>  Changes in v3:
>     - Added max member from struct rcsi2_mbps_reg.
>       mbps varialbe cannot be removed from rcsi2_mbps_reg,
>       since this structure is reused for
>       phtw_mbps_h3_v3h_m3n/phtw_mbps_v3m_e3 where mbps is
>       used.
> 
> 
>    -  Update the walk of the array in rcsi2_set_phypll() so that it finds
>       the first entry where the calculated bit rate is less than the max.
> 
>    - Support lower bit rates less than 80Mbps like 48Mbps
>      (Raspberry pi camera 640x480 connected to Kingfisher)
>      can also be supported by selecting the lowest default bit rate 80Mbps
>      as done before this fix
> 
>    - Alignement of the commit message based on above changes.
> 
>  Changes in v4:
>   -  Remove unncessary braces.
> 
>  Changes in v5:
>    - Removed mbps variable in rcsi2_mbps_reg and aligned all
>      tables accordingly
> 
> 
>  Changes in v6
>    - Renesas correct the range of default value 220Mbps. Now
>      if we select the nearest value to the default value all
>          the values are in range. So reverting back to original patch
>   
>    - Added warning for values less than Minimum 80Mbps
>       
> Changes in v7
>   - Create a seperate commit for the warning message less
>     than minimum 80Mbps 
>   
>   - Reorder the statements to increase readability
>   
> Changes in v8
>   - Extended the logic of selection of nearest mbps to
>     PHTW registers value less than 250Mbps. A new commit
>     is added
> 	
>  drivers/media/platform/rcar-vin/rcar-csi2.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/rcar-vin/rcar-csi2.c b/drivers/media/platform/rcar-vin/rcar-csi2.c
> index 151e6a9..f18dedc 100644
> --- a/drivers/media/platform/rcar-vin/rcar-csi2.c
> +++ b/drivers/media/platform/rcar-vin/rcar-csi2.c
> @@ -431,16 +431,23 @@ static int rcsi2_wait_phy_start(struct rcar_csi2 *priv)
>  static int rcsi2_set_phypll(struct rcar_csi2 *priv, unsigned int mbps)
>  {
>  	const struct rcsi2_mbps_reg *hsfreq;
> +	const struct rcsi2_mbps_reg *hsfreq_prev = NULL;
>  
> -	for (hsfreq = priv->info->hsfreqrange; hsfreq->mbps != 0; hsfreq++)
> +	for (hsfreq = priv->info->hsfreqrange; hsfreq->mbps != 0; hsfreq++) {
>  		if (hsfreq->mbps >= mbps)
>  			break;
> +		hsfreq_prev = hsfreq;
> +	}
>  
>  	if (!hsfreq->mbps) {
>  		dev_err(priv->dev, "Unsupported PHY speed (%u Mbps)", mbps);
>  		return -ERANGE;
>  	}
>  
> +	if (hsfreq_prev &&
> +	    ((mbps - hsfreq_prev->mbps) <= (hsfreq->mbps - mbps)))
> +		hsfreq = hsfreq_prev;
> +
>  	rcsi2_write(priv, PHYPLL_REG, PHYPLL_HSFREQRANGE(hsfreq->reg));
>  
>  	return 0;
> -- 
> 2.7.4
> 

-- 
Regards,
Niklas Söderlund