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Subject: Re: [PATCH] fpga: altera-cvp: Truncated bitstream error support
To:     tien.sung.ang@intel.com, mdf@kernel.org, hao.wu@intel.com,
        yilun.xu@intel.com
Cc:     linux-fpga@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20220518064844.2694651-1-tien.sung.ang@intel.com>
From:   Tom Rix <trix@redhat.com>
Message-ID: <3911c8c7-da6d-e6f2-c747-3b601d9cdacc@redhat.com>
Date:   Wed, 18 May 2022 13:08:31 -0700
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On 5/17/22 11:48 PM, tien.sung.ang@intel.com wrote:
> From: Ang Tien Sung <tien.sung.ang@intel.com>
>
> To support the error handling of a truncated bitstream sent.
> The current AIB CvP firmware is not capable of handling a
> data stream smaller than 4096bytes. The firmware's limitation
> causes a hung-up as it's DMA engine waits forever for the
> completion of the instructed 4096bytes.
> To resolve this design limitation, both firmware and CvP
> driver made several changes. At the CvP driver, we just
> have to ensure that anything lesser than 4096bytes are
> padded with extra bytes. The CvP will then, initiate the
> tear-down by clearing the START_XFER and CVP_CONFIG bits.
> We should also check for CVP_ERROR during the CvP completion.
> A send_buf which is always 4096bytes is used to copy the
> data during every transaction.
>
> Signed-off-by: Ang Tien Sung <tien.sung.ang@intel.com>
> ---
>   drivers/fpga/altera-cvp.c | 24 +++++++++++++++++++-----
>   1 file changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/fpga/altera-cvp.c b/drivers/fpga/altera-cvp.c
> index 4ffb9da537d8..80edcfb5e5fc 100644
> --- a/drivers/fpga/altera-cvp.c
> +++ b/drivers/fpga/altera-cvp.c
> @@ -81,6 +81,7 @@ struct altera_cvp_conf {
>   	u8			numclks;
>   	u32			sent_packets;
>   	u32			vsec_offset;
> +	u8			*send_buf;

Why is it necessary to hold  the send_buf in this structure ?

If it is used only in *_write, could it alloc/freed there ?

Because the write happens rarely, my preference is to alloc/free in 
*_write().

>   	const struct cvp_priv	*priv;
>   };
>   
> @@ -453,7 +454,11 @@ static int altera_cvp_write(struct fpga_manager *mgr, const char *buf,
>   		}
>   
>   		len = min(conf->priv->block_size, remaining);
> -		altera_cvp_send_block(conf, data, len);
> +		/* Copy the requested host data into the transmit buffer */
> +
> +		memcpy(conf->send_buf, data, len);
Is a memset needed for a short buffer ?
> +		altera_cvp_send_block(conf, (const u32 *)conf->send_buf,
> +		conf->priv->block_size);
>   		data += len / sizeof(u32);
>   		done += len;
>   		remaining -= len;
> @@ -492,10 +497,13 @@ static int altera_cvp_write_complete(struct fpga_manager *mgr,
>   	if (ret)
>   		return ret;
>   
> -	/* STEP 16 - check CVP_CONFIG_ERROR_LATCHED bit */
> -	altera_read_config_dword(conf, VSE_UNCOR_ERR_STATUS, &val);
> -	if (val & VSE_UNCOR_ERR_CVP_CFG_ERR) {
> -		dev_err(&mgr->dev, "detected CVP_CONFIG_ERROR_LATCHED!\n");
> +	/*
> +	 * STEP 16 - If bitstream error (truncated/miss-matched),
> +	 * we shall exit here.
> +	 */
> +	ret = altera_read_config_dword(conf, VSE_CVP_STATUS, &val);
Should this be STEP 17 ? the old 16 checked something else.

Tom

> +	if (ret || (val & VSE_CVP_STATUS_CFG_ERR)) {
> +		dev_err(&mgr->dev, "CVP_CONFIG_ERROR!\n");
>   		return -EPROTO;
>   	}
>   
> @@ -661,6 +669,12 @@ static int altera_cvp_probe(struct pci_dev *pdev,
>   
>   	pci_set_drvdata(pdev, mgr);
>   
> +	/* Allocate the 4096 block size transmit buffer */
> +	conf->send_buf = devm_kzalloc(&pdev->dev, conf->priv->block_size, GFP_KERNEL);
> +	if (!conf->send_buf) {
> +		ret = -ENOMEM;
> +		goto err_unmap;
> +	}
>   	return 0;
>   
>   err_unmap: