linux-kernel - Re: [PATCH V4 5/6] dw-hdmi: add support for multi byte register width access

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Date:	Fri, 07 Nov 2014 12:45:07 +0100
From:	Lucas Stach <l.stach@...gutronix.de>
To:	Andy Yan <andy.yan@...k-chips.com>
Cc:	airlied@...ux.ie, heiko@...ech.de, fabio.estevam@...escale.com,
	rmk+kernel@....linux.org.uk,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Grant Likely <grant.likely@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Shawn Guo <shawn.guo@...aro.org>,
	Josh Boyer <jwboyer@...hat.com>,
	Sean Paul <seanpaul@...omium.org>,
	Inki Dae <inki.dae@...sung.com>,
	Dave Airlie <airlied@...hat.com>,
	Arnd Bergmann <arnd@...db.de>, Zubair.Kakakhel@...tec.com,
	djkurtz@...gle.com, ykk@...k-chips.com,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	devel@...verdev.osuosl.org, devicetree@...r.kernel.org,
	linux-rockchip@...ts.infradead.org, jay.xu@...k-chips.com
Subject: Re: [PATCH V4 5/6] dw-hdmi: add support for multi byte register
 width access

Am Freitag, den 07.11.2014, 19:35 +0800 schrieb Andy Yan:
> On rockchip rk3288, only word(32-bit) accesses are
> permitted for hdmi registers.  Byte width access (writeb,
> readb) generates an imprecise external abort.
> 
> Signed-off-by: Andy Yan <andy.yan@...k-chips.com>
> ---
>  drivers/gpu/drm/bridge/dw_hdmi.c | 49 +++++++++++++++++++++++++++++++++++++---
>  1 file changed, 46 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/dw_hdmi.c b/drivers/gpu/drm/bridge/dw_hdmi.c
> index df76a8c..9867642 100644
> --- a/drivers/gpu/drm/bridge/dw_hdmi.c
> +++ b/drivers/gpu/drm/bridge/dw_hdmi.c
> @@ -126,19 +126,42 @@ struct dw_hdmi {
[...]
> +	u32 val;
> +
> +	if (!of_property_read_u32(np, "reg-io-width", &val)) {
> +		switch (val) {
> +		case 4:
> +			hdmi->write = dw_hdmi_writel;
> +			hdmi->read = dw_hdmi_readl;
> +			hdmi->reg_shift = 2;
> +			break;
> +		default:
> +			hdmi->write = dw_hdmi_writeb;
> +			hdmi->read = dw_hdmi_readb;
> +			hdmi->reg_shift = 0;
> +			break;
> +		}
> +	} else {
> +		hdmi->write = dw_hdmi_writeb;
> +		hdmi->read = dw_hdmi_readb;
> +		hdmi->reg_shift = 0;
> +	}
>  
>  	ddc_node = of_parse_phandle(np, "ddc-i2c-bus", 0);
>  	if (ddc_node) {

This should throw an error if the property value in devicetree is not
recognized. This could be simplified like this:

	u32 val = 1;

	// this won't touch val if it can't find the property
	of_property_read_u32(np, "reg-io-width", &val) 


	switch (val) {
	case 4:
		hdmi->write = dw_hdmi_writel;
		hdmi->read = dw_hdmi_readl;
		hdmi->reg_shift = 2;
		break;
	case 1:
		hdmi->write = dw_hdmi_writeb;
		hdmi->read = dw_hdmi_readb;
		hdmi->reg_shift = 0;
		break;
	default:
		dev_err(dev, "unrecognized value for reg-io-width");
		// error handling
	}

Also the DT binding doc for this property is missing.

Regards,
Lucas
-- 
Pengutronix e.K.             | Lucas Stach                 |
Industrial Linux Solutions   | http://www.pengutronix.de/  |

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