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

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Date:   Tue, 26 Mar 2019 09:55:29 +0200
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.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

Paolo Bonzini <pbonzini@...hat.com> writes:

> On 15/03/19 00:16, Fenghua Yu wrote:
>> 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.
>
> No, Kalle is right.  You do need to change
>
> -	u32 tmp_ch_bitmap[2];
> +	u32 tmp_ch_bitmap[2] __aligned(sizeof(unsigned long));
>
> into
>
> -	u32 tmp_ch_bitmap[2];
> +	__le32 tmp_ch_bitmap[2] __aligned(sizeof(unsigned long));
>
> The assignment from wl->reg_ch_conf_pending to tmp_ch_bitmap is fine
> because it goes through memcpy.

Thanks for confirming, I'll then drop patch 3 and wait for a new
version. IMHO it would be easier to submit this patch separately to
linux-wireless, no need to have within this bigger patchset.

-- 
Kalle Valo