linux-kernel - Re: [PATCH v2 05/20] rpmsg: glink: Allow unaligned data access

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Message-ID: <6baef774-50ed-2dc9-8aed-5e02b0bfeaa5@codeaurora.org>
Date:   Mon, 28 Aug 2017 17:16:38 +0530
From:   Arun Kumar Neelakantam <aneela@...eaurora.org>
To:     Sricharan R <sricharan@...eaurora.org>, ohad@...ery.com,
        bjorn.andersson@...aro.org, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 05/20] rpmsg: glink: Allow unaligned data access



On 8/24/2017 12:51 PM, Sricharan R wrote:
> From: Bjorn Andersson <bjorn.andersson@...aro.org>
>
> Glink protocol requires that each message is aligned
> on a 8 byte offset. This is purely a restriction
> from glink, so in order to support clients which
> do not adher to this, allow data packets of any size,
> but align the head index accordingly, effectively
> removing the alignment restriction.
>
> Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> Signed-off-by: Sricharan R <sricharan@...eaurora.org>
Acked-by: Arun Kumar Neelakantam <aneela@...eaurora.org>

Regards,
Arun N
> ---
>   drivers/rpmsg/qcom_glink_native.c |  6 ------
>   drivers/rpmsg/qcom_glink_rpm.c    | 22 +++++++++++++++++++++-
>   2 files changed, 21 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/rpmsg/qcom_glink_native.c b/drivers/rpmsg/qcom_glink_native.c
> index ffdf88e..a6394cd 100644
> --- a/drivers/rpmsg/qcom_glink_native.c
> +++ b/drivers/rpmsg/qcom_glink_native.c
> @@ -227,9 +227,6 @@ static int qcom_glink_tx(struct qcom_glink *glink,
>   	if (tlen >= glink->tx_pipe->length)
>   		return -EINVAL;
>   
> -	if (WARN(tlen % 8, "Unaligned TX request"))
> -		return -EINVAL;
> -
>   	ret = mutex_lock_interruptible(&glink->tx_lock);
>   	if (ret)
>   		return ret;
> @@ -695,9 +692,6 @@ static int __qcom_glink_send(struct glink_channel *channel,
>   		__le32 left_size;
>   	} __packed req;
>   
> -	if (WARN(len % 8, "RPM GLINK expects 8 byte aligned messages\n"))
> -		return -EINVAL;
> -
>   	req.msg.cmd = cpu_to_le16(RPM_CMD_TX_DATA);
>   	req.msg.param1 = cpu_to_le16(channel->lcid);
>   	req.msg.param2 = cpu_to_le32(channel->rcid);
> diff --git a/drivers/rpmsg/qcom_glink_rpm.c b/drivers/rpmsg/qcom_glink_rpm.c
> index 33daa32..cc73af0 100644
> --- a/drivers/rpmsg/qcom_glink_rpm.c
> +++ b/drivers/rpmsg/qcom_glink_rpm.c
> @@ -156,11 +156,31 @@ static void glink_rpm_tx_write(struct qcom_glink_pipe *glink_pipe,
>   			       const void *data, size_t dlen)
>   {
>   	struct glink_rpm_pipe *pipe = to_rpm_pipe(glink_pipe);
> +	size_t tlen = hlen + dlen;
> +	size_t aligned_dlen;
>   	unsigned int head;
> +	char padding[8] = {0};
> +	size_t pad;
> +
> +	/* Header length comes from glink native and is always 4 byte aligned */
> +	if (WARN(hlen % 4, "Glink Header length must be 4 bytes aligned\n"))
> +		return;
> +
> +	/*
> +	 * Move the unaligned tail of the message to the padding chunk, to
> +	 * ensure word aligned accesses
> +	 */
> +	aligned_dlen = ALIGN_DOWN(dlen, 4);
> +	if (aligned_dlen != dlen)
> +		memcpy(padding, data + aligned_dlen, dlen - aligned_dlen);
>   
>   	head = readl(pipe->head);
>   	head = glink_rpm_tx_write_one(pipe, head, hdr, hlen);
> -	head = glink_rpm_tx_write_one(pipe, head, data, dlen);
> +	head = glink_rpm_tx_write_one(pipe, head, data, aligned_dlen);
> +
> +	pad = ALIGN(tlen, 8) - ALIGN_DOWN(tlen, 4);
> +	if (pad)
> +		head = glink_rpm_tx_write_one(pipe, head, padding, pad);
>   	writel(head, pipe->head);
>   }
>