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




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