Re: [PATCH 3/3] PCI: imx6: Make fallthrough comments more consistent

[Bjorn Helgaas]

On Sun, Dec 16, 2018 at 03:09:16PM -0800, Andrey Smirnov wrote:
> Convert all fallthrough comments to say "fall through", as well as
> modify their placement to the point where the "break" would normally
> be.
> 
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: Fabio Estevam <fabio.estevam@xxxxxxx>
> Cc: Chris Healy <cphealy@xxxxxxxxx>
> Cc: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
> Cc: Leonard Crestez <leonard.crestez@xxxxxxx>
> Cc: "A.s. Dong" <aisheng.dong@xxxxxxx>
> Cc: Richard Zhu <hongxing.zhu@xxxxxxx>
> Cc: linux-imx@xxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: linux-pci@xxxxxxxxxxxxxxx
> Suggested-by: Bjorn Helgaas <helgaas@xxxxxxxxxx>

I didn't make it very clear, but my suggestion was really to remove
the annotation completely; see below.

> Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
> ---
>  drivers/pci/controller/dwc/pci-imx6.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-imx6.c b/drivers/pci/controller/dwc/pci-imx6.c
> index 59658577e81d..a0510e185d44 100644
> --- a/drivers/pci/controller/dwc/pci-imx6.c
> +++ b/drivers/pci/controller/dwc/pci-imx6.c
> @@ -362,7 +362,8 @@ static void imx6_pcie_assert_core_reset(struct imx6_pcie *imx6_pcie)
>  
>  	switch (imx6_pcie->variant) {
>  	case IMX7D:
> -	case IMX8MQ: /* FALLTHROUGH */
> +		/* fall through */
> +	case IMX8MQ:
>  		reset_control_assert(imx6_pcie->pciephy_reset);
>  		reset_control_assert(imx6_pcie->apps_reset);
>  		break;

IMO this use of "fall through" is superfluous and unusual in the Linux
source.

A "fall through" comment would be useful if the IMX7D case had
executable code but no "break".  Then the comment shows that the
intent was to execute *both* the IMX7D code and the IMX8MQ code and
the lack of a "break" was intentional.

In this case, the intent is to treat IMX7D and IMX8MQ the same, and
there's no executable code specifically for the IMX7D.  I think it's
easiest to read that when the list of identical cases is all together
without the comment in the middle, i.e., as

>  	case IMX7D:
> 	case IMX8MQ:
>  		reset_control_assert(imx6_pcie->pciephy_reset);

rather than this:

>  	case IMX7D:
> 		/* fall through */
> 	case IMX8MQ:
>  		reset_control_assert(imx6_pcie->pciephy_reset);