linux-kernel - Re: [PATCH v3 1/1] PCI: endpoint: pci-epf-test: Call pci_epf_test_raise

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Message-ID: <54451b81-b503-4072-807a-af2f0b914ec2@kernel.org>
Date: Tue, 20 Aug 2024 17:18:10 +0900
From: Damien Le Moal <dlemoal@...nel.org>
To: Rick Wertenbroek <rick.wertenbroek@...il.com>, rick.wertenbroek@...g-vd.ch
Cc: alberto.dassatti@...g-vd.ch,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Krzysztof Wilczyński <kw@...ux.com>,
 Kishon Vijay Abraham I <kishon@...nel.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>, Niklas Cassel <cassel@...nel.org>,
 Frank Li <Frank.Li@....com>, Lars-Peter Clausen <lars@...afoo.de>,
 linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/1] PCI: endpoint: pci-epf-test: Call
 pci_epf_test_raise_irq() on failed DMA check

On 8/20/24 16:10, Rick Wertenbroek wrote:
> The pci-epf-test PCI endpoint function /drivers/pci/endpoint/function/pci-epf_test.c
> is meant to be used in a PCI endpoint device connected to a host computer
> with the host side driver: /drivers/misc/pci_endpoint_test.c.
> 
> The host side driver can request read/write/copy transactions from the
> endpoint function and expects an IRQ from the endpoint function once
> the read/write/copy transaction is finished. These can be issued with or
> without DMA enabled. If the host side driver requests a read/write/copy
> transaction with DMA enabled and the endpoint function does not support
> DMA, the endpoint would only print an error message and wait for further
> commands without sending an IRQ because pci_epf_test_raise_irq() is
> skipped in pci_epf_test_cmd_handler(). This results in the host side
> driver hanging indefinitely waiting for the IRQ.
> 
> Call pci_epf_test_raise_irq() when a transfer with DMA is requested but
> DMA is unsupported. The host side driver will no longer hang but report
> an error on transfer (printing "NOT OKAY") thanks to the checksum because
> no data was moved.
> 
> Clarify the error message in the endpoint function as "Cannot ..." is
> vague and does not state the reason why it cannot be done.
> 
> Signed-off-by: Rick Wertenbroek <rick.wertenbroek@...il.com>
> ---
>  drivers/pci/endpoint/functions/pci-epf-test.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> index 7c2ed6eae53a..b02193cef06e 100644
> --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> @@ -649,7 +649,8 @@ static void pci_epf_test_cmd_handler(struct work_struct *work)
>  
>  	if ((READ_ONCE(reg->flags) & FLAG_USE_DMA) &&
>  	    !epf_test->dma_supported) {
> -		dev_err(dev, "Cannot transfer data using DMA\n");
> +		dev_err(dev, "DMA transfer not supported\n");

Should we set the FAIL status flag here ?
E.g.:
		 reg->status |= STATUS_READ_FAIL;

Note: I have no idea why the status flags are different for the different
operations. We should really have a single SUCCESS/FAIL flag common to all
operations. So I think we could just do:

		reg->status |= STATUS_READ_FAIL | STATUS_WRITE_FAIL |
			STATUS_COPY_FAIL;

here, or go back to your v1 and handle the failure in each operation function to
set the correct flag.

> +		pci_epf_test_raise_irq(epf_test, reg);
>  		goto reset_handler;
>  	}
>  

-- 
Damien Le Moal
Western Digital Research