linux-kernel - Re: [PATCH v5 03/18] wlcore: simplify/fix/optimize reg_ch_conf

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Date:   Thu, 14 Mar 2019 16:16:14 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Kalle Valo <kvalo@...eaurora.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>,
        Michael Chan <michael.chan@...adcom.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        x86 <x86@...nel.org>, linux-wireless@...r.kernel.org,
        netdev@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v5 03/18] wlcore: simplify/fix/optimize
 reg_ch_conf_pending operations

Hi, Valo,

On Thu, Mar 14, 2019 at 03:16:33PM +0200, Kalle Valo wrote:
> Fenghua Yu <fenghua.yu@...el.com> writes:
> 
> > From: Paolo Bonzini <pbonzini@...hat.com>
> >
> > Bitmaps are defined on unsigned longs, so the usage of u32[2] in the
> > wlcore driver is incorrect.  As noted by Peter Zijlstra, casting arrays
> > to a bitmap is incorrect for big-endian architectures.
> >
> > When looking at it I observed that:
> >
> > - operations on reg_ch_conf_pending is always under the wl_lock mutex,
> > so set_bit is overkill
> >
> > - the only case where reg_ch_conf_pending is accessed a u32 at a time is
> > unnecessary too.
> >
> > This patch cleans up everything in this area, and changes tmp_ch_bitmap
> > to have the proper alignment.
> >
> > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> 
> [...]
> 
> >  int wlcore_cmd_regdomain_config_locked(struct wl1271 *wl)
> >  {
> >  	struct wl12xx_cmd_regdomain_dfs_config *cmd = NULL;
> >  	int ret = 0, i, b, ch_bit_idx;
> > -	u32 tmp_ch_bitmap[2];
> > +	u32 tmp_ch_bitmap[2] __aligned(sizeof(unsigned long));
> >  	struct wiphy *wiphy = wl->hw->wiphy;
> >  	struct ieee80211_supported_band *band;
> >  	bool timeout = false;
> 
> [...]
> 
> > @@ -1754,8 +1751,8 @@ int wlcore_cmd_regdomain_config_locked(struct wl1271 *wl)
> >  		goto out;
> >  	}
> >  
> > -	cmd->ch_bit_map1 = cpu_to_le32(tmp_ch_bitmap[0]);
> > -	cmd->ch_bit_map2 = cpu_to_le32(tmp_ch_bitmap[1]);
> > +	cmd->ch_bit_map1 = tmp_ch_bitmap[0];
> > +	cmd->ch_bit_map2 = tmp_ch_bitmap[1];
> 
> Will sparse still be happy? AFAICS you are now assigning u32 to __le32:
> 
> struct wl12xx_cmd_regdomain_dfs_config {
>        struct wl1271_cmd_header header;
> 
>        __le32 ch_bit_map1;
>        __le32 ch_bit_map2;

Discussion between Peter and Paolo (https://lkml.org/lkml/2019/3/4/521)
may answer your question.

(Sorry I didn't send to you v4 patch set)

> 
> Also this doesn't depend on anything else from this patchset, right? So
> I could apply this directly?

You are right. This patch doesn't rely on other patches from this patchset.
This patch just fixes a split lock issue. You could apply this directly
without other patches.

Thanks.

-Fenghua