linux-kernel - Re: [PATCH] video: imxfb: correct the bitmask for DMACR_HM/

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Date:   Wed, 23 Nov 2016 10:31:13 +0100
From:   Martin Kaiser <martin@...ser.cx>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Sascha Hauer <kernel@...gutronix.de>, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] video: imxfb: correct the bitmask for DMACR_HM/_TM

Hello Uwe, all,

Thus wrote Uwe Kleine-König (u.kleine-koenig@...gutronix.de):

> For the MX1 which is also supported by this driver, the definitions are
> right.

ok, understood. I wasn't able to dig up an imx1 specification. Do you
know if it's publicly available?

> So this needs a more sophisticated patch. Also I wonder why the
> register definition is in include/linux/platform_data and not in the
> driver directly.

The DMACR_HM() and _TM() macros are meant to be used when we initialize
imx_fb_platform_data's dmacr component for a platform device. It's not
straightforward to distinguish between imx1 and imx21 at initialization
time.

We could modify imx_fb_platform_data to use different components for
dmacr_burst, dmacr_hm, dmacr_tm and calculate the dmacr register value
in the driver where is_imx1_fb() is available. Device tree is also using
a single dmacr entry, it's probably not a good idea to do this
differently for platform devices...

We could also define DMACR_HM_IMX1(), DMACR_HM_IMX21(), ...

Or we could just remove the macros, they are not used by any boards in
the mainline kernel. If we don't want to break proprietary board
definitions, we could at least add a comment that the macros are
incorrect for imx21.

Thoughts?

Best regards,
Martin