Re: [PATCH v13 07/12] drm: bridge/dw_hdmi: add support for multi-byte register width access

From: Andy Yan <andy.yan@rock-chips.com>
To: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>,
	heiko@sntech.de, airlied@linux.ie,
	dri-devel@lists.freedesktop.org, ykk@rock-chips.com,
	devel@driverdev.osuosl.org, Arnd Bergmann <arnd@arndb.de>,
	linux-rockchip@lists.infradead.org,
	Grant Likely <grant.likely@linaro.org>,
	rmk+kernel@arm.linux.org.uk, jay.xu@rock-chips.com,
	devicetree@vger.kernel.org, Zubair.Kakakhel@imgtec.com,
	Pawel Moll <pawel.moll@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Inki Dae <inki.dae@samsung.com>, Rob Herring <robh+dt@kernel.org>,
	Sean Paul <seanpaul@chromium.org>,
	Dave Airlie <airlied@redhat.com>,
	mark.yao@rock-chips.com, fabio.estevam@freescale.com,
	Josh Boyer <jwboyer@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-kernel@vger.kernel.org, djkurtz@google.com,
	Kumar Gala <galak@codeaurora.org>,
	Shawn Guo <shawn.guo@linaro.org>,
	Lucas Stach <l.stach@pengutronix.de>
Subject: Re: [PATCH v13 07/12] drm: bridge/dw_hdmi: add support for multi-byte register width access
Date: Mon, 01 Dec 2014 20:46:36 +0800	[thread overview]
Message-ID: <547C632C.7000309@rock-chips.com> (raw)
In-Reply-To: <1417435456.4624.12.camel@pengutronix.de>

Hi Philipp:
On 2014年12月01日 20:04, Philipp Zabel wrote:
> Am Freitag, den 28.11.2014, 17:43 +0800 schrieb Andy Yan:
>> Hi Zabel:
>> On 2014年11月27日 00:34, Philipp Zabel wrote:
>>> Am Mittwoch, den 26.11.2014, 21:32 +0800 schrieb Andy Yan:
>>>> On rockchip rk3288, only word(32-bit) accesses are
>>>> permitted for hdmi registers.  Byte width accesses (writeb,
>>>> readb) generate an imprecise external abort.
>>>>
>>>> Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
>>>>
>>>> ---
>>>>
>>>> Changes in v13: None
>>>> Changes in v12: None
>>>> Changes in v11: None
>>>> Changes in v10: None
>>>> Changes in v9: None
>>>> Changes in v8: None
>>>> Changes in v7: None
>>>> Changes in v6:
>>>> - refactor register access without reg_shift
>>>>
>>>> Changes in v5:
>>>> - refactor reg-io-width
>>>>
>>>> Changes in v4: None
>>>> Changes in v3:
>>>> - split multi-register access to one indepent patch
>>>>
>>>>    drivers/gpu/drm/bridge/dw_hdmi.c | 57 +++++++++++++++++++++++++++++++++++-----
>>>>    1 file changed, 51 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/bridge/dw_hdmi.c b/drivers/gpu/drm/bridge/dw_hdmi.c
>>>> index a53bf63..5e88c8d 100644
>>>> --- a/drivers/gpu/drm/bridge/dw_hdmi.c
>>>> +++ b/drivers/gpu/drm/bridge/dw_hdmi.c
>>>> @@ -100,6 +100,11 @@ struct hdmi_data_info {
>>>>    	struct hdmi_vmode video_mode;
>>>>    };
>>>>    
>>>> +union dw_reg_ptr {
>>>> +	u32 __iomem *p32;
>>>> +	u8 __iomem *p8;
>>>> +};
>>> I see no need to introduce this. Just explicitly multiply the offset in
>>> dw_hdmi_writel.
>>>
>>       Is there any disadvantage to do like this?
>>       The compiler can help us do the explicitly multiply by this way.
> Four additional lines, a new defined type, a few more changes to struct
> dw_hdmi and dw_hdmi_bind necessary.
>
> Technically I see no problem to let the compiler do the multiplication,
> my issue is that it ever so slightly obfuscates the code. Instead of
> just writing "* 4" in two functions, we get a new union that you need to
> know about when looking at struct dw_hdmi and dw_hdmi_bind, regs.p8 is
> used but never assigned directly, it's just a tiny bit of additional
> effort needed to understand the code. But when the cost to avoid that is
> so small...
>
> regards
> Philipp
>

   What you said is right, I will change it in PATCH V15
    thanks .
> _______________________________________________
> Linux-rockchip mailing list
> Linux-rockchip@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-rockchip


_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel