linux-kernel - Re: [PATCH] PCI: designware-ep: use ffz() instead of find_first_zero

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Date:   Fri, 17 Nov 2017 11:38:35 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Niklas Cassel <niklas.cassel@...s.com>
Cc:     Jingoo Han <jingoohan1@...il.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Niklas Cassel <niklass@...s.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: designware-ep: use ffz() instead of
 find_first_zero_bit()

Please follow Bjorn's request for patch formatting:

https://marc.info/?l=linux-pci&m=150905742808166&w=2

I would mention in the commit title that this is a fix.

eg "PCI: designware-ep: Fix find_first_zero_bit() usage"

On Thu, Nov 16, 2017 at 07:34:38PM +0100, Niklas Cassel wrote:
> find_first_zero_bit()'s parameter 'size' is defined in bits,
> not in bytes.
> 
> find_first_zero_bit() was called with bytes rather than bits,

"was called with size in bytes"...

> which thus defined a too low upper limit, causing
> dw_pcie_ep_inbound_atu() to assign iatu index #4 to both bar 4
> and bar 5, which made bar 5 overwrite the settings set by bar 4.
> 
> ./pcitest.sh
> BAR tests
> BAR0:		OKAY
> BAR1:		OKAY
> BAR2:		OKAY
> BAR3:		OKAY
> BAR4:		NOT OKAY
> BAR5:		OKAY

Sorry but this example is pretty much useless - either you add
a self-explanatory kernel log or you just remove it.

> Fix this by using replacing find_first_zero_bit() with ffz(),
> since ffz() only works on a single 'unsigned long' and therefore
> does not need a size argument.
> 
> Signed-off-by: Niklas Cassel <niklas.cassel@...s.com>

We need a Fixes: tag at least, see Bjorn's post above.

Thanks,
Lorenzo

> ---
>  drivers/pci/dwc/pcie-designware-ep.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/dwc/pcie-designware-ep.c b/drivers/pci/dwc/pcie-designware-ep.c
> index d53d5f168363..ab9a9e160daf 100644
> --- a/drivers/pci/dwc/pcie-designware-ep.c
> +++ b/drivers/pci/dwc/pcie-designware-ep.c
> @@ -70,8 +70,7 @@ static int dw_pcie_ep_inbound_atu(struct dw_pcie_ep *ep, enum pci_barno bar,
>  	u32 free_win;
>  	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
>  
> -	free_win = find_first_zero_bit(&ep->ib_window_map,
> -				       sizeof(ep->ib_window_map));
> +	free_win = ffz(ep->ib_window_map);
>  	if (free_win >= ep->num_ib_windows) {
>  		dev_err(pci->dev, "no free inbound window\n");
>  		return -EINVAL;
> @@ -96,8 +95,7 @@ static int dw_pcie_ep_outbound_atu(struct dw_pcie_ep *ep, phys_addr_t phys_addr,
>  	u32 free_win;
>  	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
>  
> -	free_win = find_first_zero_bit(&ep->ob_window_map,
> -				       sizeof(ep->ob_window_map));
> +	free_win = ffz(ep->ob_window_map);
>  	if (free_win >= ep->num_ob_windows) {
>  		dev_err(pci->dev, "no free outbound window\n");
>  		return -EINVAL;
> -- 
> 2.14.2
>