netdev - Re: [PATCH v10 1/1] can: usb: etas_es58X: add support for ETAS ES58X CAN USB interfaces

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Message-ID: <a0ea23cb-cf97-ca0b-be88-74c20bedc869@pengutronix.de>
Date:   Wed, 13 Jan 2021 17:06:03 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Vincent MAILHOL <mailhol.vincent@...adoo.fr>
Cc:     linux-can <linux-can@...r.kernel.org>,
        Arunachalam Santhanam <arunachalam.santhanam@...bosch.com>,
        Wolfgang Grandegger <wg@...ndegger.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jimmy Assarsson <extja@...ser.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        "open list : NETWORKING DRIVERS" <netdev@...r.kernel.org>
Subject: Re: [PATCH v10 1/1] can: usb: etas_es58X: add support for ETAS ES58X
 CAN USB interfaces

On 1/13/21 3:35 PM, Vincent MAILHOL wrote:
>> My understanding is that having a queue size being a power of two is
>> required in order not to use spinlocks (else, modulo operations would
>> break when the index wraparound back to zero). I tried to minimize the
>> number of spinlock: only one per bulk send or bulk receive.
> 
> Or do you mean to round up the skb_echo array length to the next power
> of two in the driver despite the actual size of the device FIFO? Did
> not think about that in the past but that should work.
> 
> I am going to think a bit more of how to improve that.

For the echo_skb rounding up might work, but you should round down, so that your
can directly use the masked value.

Marc
-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
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