linux-kernel - Re: [PATCH 1/2] mailbox: ti-msgmgr: Refactor message read during interrupt handler

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Message-ID: <073d7213-bd3a-5adb-8187-f0a83478fd76@ti.com>
Date:   Fri, 25 Feb 2022 18:16:07 -0600
From:   Suman Anna <s-anna@...com>
To:     Dave Gerlach <d-gerlach@...com>,
        Jassi Brar <jassisinghbrar@...il.com>
CC:     <linux-kernel@...r.kernel.org>, Nishanth Menon <nm@...com>,
        Vignesh Raghavendra <vigneshr@...com>
Subject: Re: [PATCH 1/2] mailbox: ti-msgmgr: Refactor message read during
 interrupt handler

On 2/9/22 22:16, Dave Gerlach wrote:
> Refactor the portion of code that actually reads received messages from
> a queue into its own function, ti_msgmgr_queue_rx_data, that is called
> by the interrupt handler instead of reading directly from the handler.
> 
> Signed-off-by: Dave Gerlach <d-gerlach@...com>

Acked-by: Suman Anna <s-anna@...com>

> ---
>  drivers/mailbox/ti-msgmgr.c | 88 +++++++++++++++++++++----------------
>  1 file changed, 49 insertions(+), 39 deletions(-)
> 
> diff --git a/drivers/mailbox/ti-msgmgr.c b/drivers/mailbox/ti-msgmgr.c
> index efb43b038596..f860cd0c907a 100644
> --- a/drivers/mailbox/ti-msgmgr.c
> +++ b/drivers/mailbox/ti-msgmgr.c
> @@ -190,6 +190,53 @@ static inline bool ti_msgmgr_queue_is_error(const struct ti_msgmgr_desc *d,
>  	return val ? true : false;
>  }
>  
> +static int ti_msgmgr_queue_rx_data(struct mbox_chan *chan, struct ti_queue_inst *qinst,
> +				   const struct ti_msgmgr_desc *desc)
> +{
> +	int num_words;
> +	struct ti_msgmgr_message message;
> +	void __iomem *data_reg;
> +	u32 *word_data;
> +
> +	/*
> +	 * I have no idea about the protocol being used to communicate with the
> +	 * remote producer - 0 could be valid data, so I wont make a judgement
> +	 * of how many bytes I should be reading. Let the client figure this
> +	 * out.. I just read the full message and pass it on..
> +	 */
> +	message.len = desc->max_message_size;
> +	message.buf = (u8 *)qinst->rx_buff;
> +
> +	/*
> +	 * NOTE about register access involved here:
> +	 * the hardware block is implemented with 32bit access operations and no
> +	 * support for data splitting.  We don't want the hardware to misbehave
> +	 * with sub 32bit access - For example: if the last register read is
> +	 * split into byte wise access, it can result in the queue getting
> +	 * stuck or indeterminate behavior. An out of order read operation may
> +	 * result in weird data results as well.
> +	 * Hence, we do not use memcpy_fromio or __ioread32_copy here, instead
> +	 * we depend on readl for the purpose.
> +	 *
> +	 * Also note that the final register read automatically marks the
> +	 * queue message as read.
> +	 */
> +	for (data_reg = qinst->queue_buff_start, word_data = qinst->rx_buff,
> +	     num_words = (desc->max_message_size / sizeof(u32));
> +	     num_words; num_words--, data_reg += sizeof(u32), word_data++)
> +		*word_data = readl(data_reg);
> +
> +	/*
> +	 * Last register read automatically clears the IRQ if only 1 message
> +	 * is pending - so send the data up the stack..
> +	 * NOTE: Client is expected to be as optimal as possible, since
> +	 * we invoke the handler in IRQ context.
> +	 */
> +	mbox_chan_received_data(chan, (void *)&message);
> +
> +	return 0;
> +}
> +
>  /**
>   * ti_msgmgr_queue_rx_interrupt() - Interrupt handler for receive Queue
>   * @irq:	Interrupt number
> @@ -206,10 +253,7 @@ static irqreturn_t ti_msgmgr_queue_rx_interrupt(int irq, void *p)
>  	struct ti_msgmgr_inst *inst = dev_get_drvdata(dev);
>  	struct ti_queue_inst *qinst = chan->con_priv;
>  	const struct ti_msgmgr_desc *desc;
> -	int msg_count, num_words;
> -	struct ti_msgmgr_message message;
> -	void __iomem *data_reg;
> -	u32 *word_data;
> +	int msg_count;
>  
>  	if (WARN_ON(!inst)) {
>  		dev_err(dev, "no platform drv data??\n");
> @@ -237,41 +281,7 @@ static irqreturn_t ti_msgmgr_queue_rx_interrupt(int irq, void *p)
>  		return IRQ_NONE;
>  	}
>  
> -	/*
> -	 * I have no idea about the protocol being used to communicate with the
> -	 * remote producer - 0 could be valid data, so I won't make a judgement
> -	 * of how many bytes I should be reading. Let the client figure this
> -	 * out.. I just read the full message and pass it on..
> -	 */
> -	message.len = desc->max_message_size;
> -	message.buf = (u8 *)qinst->rx_buff;
> -
> -	/*
> -	 * NOTE about register access involved here:
> -	 * the hardware block is implemented with 32bit access operations and no
> -	 * support for data splitting.  We don't want the hardware to misbehave
> -	 * with sub 32bit access - For example: if the last register read is
> -	 * split into byte wise access, it can result in the queue getting
> -	 * stuck or indeterminate behavior. An out of order read operation may
> -	 * result in weird data results as well.
> -	 * Hence, we do not use memcpy_fromio or __ioread32_copy here, instead
> -	 * we depend on readl for the purpose.
> -	 *
> -	 * Also note that the final register read automatically marks the
> -	 * queue message as read.
> -	 */
> -	for (data_reg = qinst->queue_buff_start, word_data = qinst->rx_buff,
> -	     num_words = (desc->max_message_size / sizeof(u32));
> -	     num_words; num_words--, data_reg += sizeof(u32), word_data++)
> -		*word_data = readl(data_reg);
> -
> -	/*
> -	 * Last register read automatically clears the IRQ if only 1 message
> -	 * is pending - so send the data up the stack..
> -	 * NOTE: Client is expected to be as optimal as possible, since
> -	 * we invoke the handler in IRQ context.
> -	 */
> -	mbox_chan_received_data(chan, (void *)&message);
> +	ti_msgmgr_queue_rx_data(chan, qinst, desc);
>  
>  	return IRQ_HANDLED;
>  }