linux-kernel - Re: [PATCH v4 13/27] bus: mhi: ep: Add support for managing MMIO registers

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Date:   Mon, 28 Feb 2022 10:23:52 -0600
From:   Alex Elder <elder@...aro.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        mhi@...ts.linux.dev
Cc:     quic_hemantk@...cinc.com, quic_bbhatt@...cinc.com,
        quic_jhugo@...cinc.com, vinod.koul@...aro.org,
        bjorn.andersson@...aro.org, dmitry.baryshkov@...aro.org,
        quic_vbadigan@...cinc.com, quic_cang@...cinc.com,
        quic_skananth@...cinc.com, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 13/27] bus: mhi: ep: Add support for managing MMIO
 registers

On 2/28/22 6:43 AM, Manivannan Sadhasivam wrote:
> Add support for managing the Memory Mapped Input Output (MMIO) registers
> of the MHI bus. All MHI operations are carried out using the MMIO registers
> by both host and the endpoint device.
> 
> The MMIO registers reside inside the endpoint device memory (fixed
> location based on the platform) and the address is passed by the MHI EP
> controller driver during its registration.

I thought it might have been a mistake that MHI_MASK_ROWS_CH_EV_DB
was used when iterating over channels and events.  Now I see it
represents the number of "rows" of 32-bit doorbell registers for
either events or channels.

I guess it might be reasonable to assume the number of event "rows"
is the same as the number of channel rows.  But *maybe* consider
defining them separately, like:
   MHI_MASK_ROWS_CH_DB
   MHI_MASK_ROWS_EV_DB

I also have one more comment below.

Whether or not you implement one or both of these suggestions:

Reviewed-by: Alex Elder <elder@...aro.org>

> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> ---
>   drivers/bus/mhi/ep/Makefile   |   2 +-
>   drivers/bus/mhi/ep/internal.h |  26 ++++
>   drivers/bus/mhi/ep/main.c     |   6 +-
>   drivers/bus/mhi/ep/mmio.c     | 272 ++++++++++++++++++++++++++++++++++
>   include/linux/mhi_ep.h        |  18 +++
>   5 files changed, 322 insertions(+), 2 deletions(-)
>   create mode 100644 drivers/bus/mhi/ep/mmio.c
> 

. . .

> diff --git a/drivers/bus/mhi/ep/mmio.c b/drivers/bus/mhi/ep/mmio.c
> new file mode 100644
> index 000000000000..311c5d94c4d2
> --- /dev/null
> +++ b/drivers/bus/mhi/ep/mmio.c
> @@ -0,0 +1,272 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Linaro Ltd.
> + * Author: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/io.h>
> +#include <linux/mhi_ep.h>
> +
> +#include "internal.h"
> +

. . .

> +bool mhi_ep_mmio_read_chdb_status_interrupts(struct mhi_ep_cntrl *mhi_cntrl)
> +{
> +	bool chdb = 0;
> +	u32 i;
> +
> +	for (i = 0; i < MHI_MASK_ROWS_CH_EV_DB; i++) {
> +		mhi_cntrl->chdb[i].status = mhi_ep_mmio_read(mhi_cntrl, MHI_CHDB_INT_STATUS_n(i));
> +		chdb |= !!mhi_cntrl->chdb[i].status;

This is fine, but I think I'd prefer this to be:

		if (mhi_cntrl->chdb[i].status)
			chdb = true;

Because you're using a bitwise operator to set a Boolean value.


> +	}
> +
> +	/* Return whether a channel doorbell interrupt occurred or not */
> +	return chdb;
> +}
> +

. . .