linux-kernel - Re: [PATCHv5] drivers/amba: add reset control to amba bus probe

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Date:   Tue, 27 Aug 2019 15:25:24 -0400
From:   "Valdis Klētnieks" <valdis.kletnieks@...edu>
To:     Dinh Nguyen <dinguyen@...nel.org>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        robh@...nel.org, linux@...linux.org.uk, frowand.list@...il.com,
        keescook@...omium.org, anton@...msg.org, ccross@...roid.com,
        tony.luck@...el.com, daniel.thompson@...aro.org,
        linus.walleij@...aro.org, manivannan.sadhasivam@...aro.org,
        linux-arm-kernel@...ts.infradead.org, p.zabel@...gutronix.de
Subject: Re: [PATCHv5] drivers/amba: add reset control to amba bus probe

On Mon, 26 Aug 2019 10:42:52 -0500, Dinh Nguyen said:
> The primecell controller on some SoCs, i.e. SoCFPGA, is held in reset by
> default. Until recently, the DMA controller was brought out of reset by the
> bootloader(i.e. U-Boot). But a recent change in U-Boot, the peripherals
> that are not used are held in reset and are left to Linux to bring them
> out of reset.
>
> Add a mechanism for getting the reset property and de-assert the primecell
> module from reset if found. This is a not a hard fail if the reset properti
> is not present in the device tree node, so the driver will continue to
> probe.

Does this DTRT for both old and new U-Boots? My naive reading of this patch
says on an old U-Boot, we end up attempting to bring it out of reset even though
they had already been brought out.

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