linux-kernel - Re: [PATCH] fpga: altera-cvp: Truncated bitstream error support

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Date:   Sat, 28 May 2022 18:03:09 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     Tom Rix <trix@...hat.com>
Cc:     tien.sung.ang@...el.com, mdf@...nel.org, hao.wu@...el.com,
        linux-fpga@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fpga: altera-cvp: Truncated bitstream error support

On Wed, May 18, 2022 at 01:08:31PM -0700, Tom Rix wrote:
> 
> On 5/17/22 11:48 PM, tien.sung.ang@...el.com wrote:
> > From: Ang Tien Sung <tien.sung.ang@...el.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@...el.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().

Is it better alloc in write_init()?

Thanks,
Yilun

> 
> >   	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: