linux-kernel - Re: [PATCH] iommu/amd: Fix extended features logging

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Message-ID: <6fbc8d6b885771ad4e69fc6789d07fd2b66f01d5.camel@perches.com>
Date:   Sun, 11 Apr 2021 04:31:06 -0700
From:   Joe Perches <joe@...ches.com>
To:     Alexander Monakov <amonakov@...ras.ru>,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>
Cc:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Joerg Roedel <jroedel@...e.de>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        iommu@...ts.linux-foundation.org
Subject: Re: [PATCH] iommu/amd: Fix extended features logging

(cc'ing the printk maintainers)

On Sun, 2021-04-11 at 00:11 +0300, Alexander Monakov wrote:
> print_iommu_info prints the EFR register and then the decoded list of
> features on a separate line:
> 
> pci 0000:00:00.2: AMD-Vi: Extended features (0x206d73ef22254ade):
>  PPR X2APIC NX GT IA GA PC GA_vAPIC
> 
> The second line is emitted via 'pr_cont', which causes it to have a
> different ('warn') loglevel compared to the previous line ('info').
> 
> Commit 9a295ff0ffc9 attempted to rectify this by removing the newline
> from the pci_info format string, but this doesn't work, as pci_info
> calls implicitly append a newline anyway.
> 
> Restore the newline, and call pr_info with empty format string to set
> the loglevel for subsequent pr_cont calls. The same solution is used in
> EFI and uvesafb drivers.
> 
> Fixes: 9a295ff0ffc9 ("iommu/amd: Print extended features in one line to fix divergent log levels")
> Signed-off-by: Alexander Monakov <amonakov@...ras.ru>
> Cc: Paul Menzel <pmenzel@...gen.mpg.de>
> Cc: Joerg Roedel <jroedel@...e.de>
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> Cc: iommu@...ts.linux-foundation.org
> ---
>  drivers/iommu/amd/init.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 596d0c413473..a25e241eff1c 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -1929,8 +1929,11 @@ static void print_iommu_info(void)
>  		pci_info(pdev, "Found IOMMU cap 0x%hx\n", iommu->cap_ptr);
>  
> 
>  		if (iommu->cap & (1 << IOMMU_CAP_EFR)) {
> -			pci_info(pdev, "Extended features (%#llx):",
> +			pci_info(pdev, "Extended features (%#llx):\n",
>  				 iommu->features);
> +
> +			pr_info("");
> +
>  			for (i = 0; i < ARRAY_SIZE(feat_str); ++i) {
>  				if (iommu_feature(iommu, (1ULL << i)))
>  					pr_cont(" %s", feat_str[i]);

This shouldn't be necessary.
If this is true then a lot of output logging code broke.