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

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Message-ID: <545D8BCE.1030202@rock-chips.com>
Date:	Sat, 08 Nov 2014 11:19:42 +0800
From:	Andy Yan <andy.yan@...k-chips.com>
To:	Lucas Stach <l.stach@...gutronix.de>
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


On 2014年11月07日 19:45, Lucas Stach wrote:
> 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
thanks for your suggestion, I will take it.
this properity is optional, I will add it to DT binding doc

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