netdev - Re: [PATCH v3] wwan: core: Support slicing in port TX flow of WWAN subsystem

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Date:   Mon, 14 Nov 2022 11:23:19 +0000
From:   Haozhe Chang (常浩哲) 
        <Haozhe.Chang@...iatek.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "stephan@...hold.net" <stephan@...hold.net>,
        "oneukum@...e.com" <oneukum@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-remoteproc@...r.kernel.org" <linux-remoteproc@...r.kernel.org>,
        "linuxwwan@...el.com" <linuxwwan@...el.com>,
        "m.chetan.kumar@...el.com" <m.chetan.kumar@...el.com>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        Hua Yang (杨华) <Hua.Yang@...iatek.com>,
        "chiranjeevi.rapolu@...ux.intel.com" 
        <chiranjeevi.rapolu@...ux.intel.com>,
        Haijun Liu (刘海军) 
        <haijun.liu@...iatek.com>,
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        "kuba@...nel.org" <kuba@...nel.org>,
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        "chandrashekar.devegowda@...el.com" 
        <chandrashekar.devegowda@...el.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "shangxiaojing@...wei.com" <shangxiaojing@...wei.com>,
        Lambert Wang (王伟) 
        <Lambert.Wang@...iatek.com>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "ricardo.martinez@...ux.intel.com" <ricardo.martinez@...ux.intel.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Xiayu Zhang (张夏宇) 
        <Xiayu.Zhang@...iatek.com>
Subject: Re: [PATCH v3] wwan: core: Support slicing in port TX flow of WWAN
 subsystem

Hi Greg Kroah-Hartman

On Fri, 2022-11-11 at 16:02 +0100, Greg Kroah-Hartman wrote:
> On Fri, Nov 11, 2022 at 06:08:36PM +0800, haozhe.chang@...iatek.com
> wrote:
> > From: haozhe chang <haozhe.chang@...iatek.com>
> > 
> > wwan_port_fops_write inputs the SKB parameter to the TX callback of
> > the WWAN device driver. However, the WWAN device (e.g., t7xx) may
> > have an MTU less than the size of SKB, causing the TX buffer to be
> > sliced and copied once more in the WWAN device driver.
> > 
> > This patch implements the slicing in the WWAN subsystem and gives
> > the WWAN devices driver the option to slice(by frag_len) or not. By
> > doing so, the additional memory copy is reduced.
> > 
> > Meanwhile, this patch gives WWAN devices driver the option to
> > reserve
> > headroom in fragments for the device-specific metadata.
> > 
> > Signed-off-by: haozhe chang <haozhe.chang@...iatek.com>
> > 
> > ---
> > Changes in v2
> >   -send fragments to device driver by skb frag_list.
> > 
> > Changes in v3
> >   -move frag_len and headroom_len setting to wwan_create_port.
> > ---
> >  drivers/net/wwan/iosm/iosm_ipc_port.c  |  3 +-
> >  drivers/net/wwan/mhi_wwan_ctrl.c       |  2 +-
> >  drivers/net/wwan/rpmsg_wwan_ctrl.c     |  2 +-
> >  drivers/net/wwan/t7xx/t7xx_port_wwan.c | 34 +++++++--------
> >  drivers/net/wwan/wwan_core.c           | 59 ++++++++++++++++++++
> > ------
> >  drivers/net/wwan/wwan_hwsim.c          |  2 +-
> >  drivers/usb/class/cdc-wdm.c            |  2 +-
> >  include/linux/wwan.h                   |  6 ++-
> >  8 files changed, 73 insertions(+), 37 deletions(-)
> > 
> > diff --git a/drivers/net/wwan/iosm/iosm_ipc_port.c
> > b/drivers/net/wwan/iosm/iosm_ipc_port.c
> > index b6d81c627277..dc43b8f0d1af 100644
> > --- a/drivers/net/wwan/iosm/iosm_ipc_port.c
> > +++ b/drivers/net/wwan/iosm/iosm_ipc_port.c
> > @@ -63,7 +63,8 @@ struct iosm_cdev *ipc_port_init(struct iosm_imem
> > *ipc_imem,
> >  	ipc_port->ipc_imem = ipc_imem;
> >  
> >  	ipc_port->iosm_port = wwan_create_port(ipc_port->dev,
> > port_type,
> > -					       &ipc_wwan_ctrl_ops,
> > ipc_port);
> > +					       &ipc_wwan_ctrl_ops, 0,
> > 0,
> > +					       ipc_port);
> 
> How is 0, 0 a valid option here?
> 
> and if it is a valid option, shouldn't you just have 2 different
> functions, one that needs these values and one that does not?  That
> would make it more descriptive as to what those options are, and
> ensure
> that you get them right.
> 
0 is a valid option. 
frag_len set to 0 means no split, and headroom set to 0 means no 
reserved headroom in skb. 

Sorry, I can't understand why it's more descriptive, could you help
with more information? It seems to me that the device driver needs to
know what each parameter is and how to set them, and that process is
also required in your proposed solution - "with 2 different functions",
right?
> > @@ -112,7 +117,6 @@ void wwan_port_rx(struct wwan_port *port,
> > struct sk_buff *skb);
> >   */
> >  void wwan_port_txoff(struct wwan_port *port);
> >  
> > -
> >  /**
> 
> Unneeded change.
> 
Yes, I will rollback it.
> thanks,
> 
> greg k-h