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    SubjectRe: [PATCH 05/16] bus: mhi: core: Add support for ringing channel/event ring doorbells
    On Thu, Jan 23, 2020 at 12:19 PM Manivannan Sadhasivam
    <manivannan.sadhasivam@linaro.org> wrote:

    > +int __must_check mhi_read_reg(struct mhi_controller *mhi_cntrl,
    > + void __iomem *base, u32 offset, u32 *out)
    > +{
    > + u32 tmp = readl_relaxed(base + offset);
    ....
    > +void mhi_write_reg(struct mhi_controller *mhi_cntrl, void __iomem *base,
    > + u32 offset, u32 val)
    > +{
    > + writel_relaxed(val, base + offset);

    Please avoid using _relaxed accessors by default, and use the regular
    ones instead. There are a number of things that can go wrong with
    the relaxed version, so ideally each caller should have a comment
    explaining why this instance is safe without the barriers and why it
    matters to not have it.

    If there are performance critical callers of mhi_read_reg/mhi_write_reg,
    you could add mhi_read_reg_relaxed/mhi_write_reg_relaxed for those
    and apply the same rules there.

    Usually most mmio accesses are only needed for reconfiguration or
    other slow paths.

    Arnd

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