lkml.org 
[lkml]   [2021]   [Jul]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v12] i2c: virtio: add a virtio i2c frontend driver
On 05-07-21, 14:22, Jie Deng wrote:
> On 2021/7/5 12:38, Viresh Kumar wrote:
> > On 05-07-21, 11:45, Jie Deng wrote:
> > > On 2021/7/5 10:40, Viresh Kumar wrote:
> > > > On 02-07-21, 16:46, Jie Deng wrote:
> > > > The right way of doing this is is making this function return - Error on failure
> > > > and 0 on success. There is no point returning number of successful additions
> > > > here.
> > >
> > > We need the number for virtio_i2c_complete_reqs to do cleanup. We don't have
> > > to
> > >
> > > do cleanup "num" times every time. Just do it as needed.
> > If you do full cleanup here, then you won't required that at the caller site.
> >
> > > > Moreover, on failures this needs to clean up (free the dmabufs) itself, just
> > > > like you did i2c_put_dma_safe_msg_buf() at the end. The caller shouldn't be
> > > > required to handle the error cases by freeing up resources.
> > >
> > > This function will return the number of requests being successfully prepared
> > > and make sure
> > >
> > > resources of the failed request being freed. And virtio_i2c_complete_reqs
> > > will free the
> > >
> > > resources of those successful request.
> > It just looks cleaner to give such responsibility to each and every function,
> > i.e. if they fail, they should clean stuff up instead of the caller. That's the
> > normal philosophy you will find across kernel in most of the cases.
> > > > > + /*
> > > > > + * Condition (req && req == &reqs[i]) should always meet since
> > > > > + * we have total nr requests in the vq.
> > > > > + */
> > > > > + if (!failed && (WARN_ON(!(req && req == &reqs[i])) ||
> > > > > + (req->in_hdr.status != VIRTIO_I2C_MSG_OK)))
> > > > What about writing this as:
> > > >
> > > > if (!failed && (WARN_ON(req != &reqs[i]) ||
> > > > (req->in_hdr.status != VIRTIO_I2C_MSG_OK)))
> > > >
> > > > We don't need to check req here since if req is NULL, we will not do req->in_hdr
> > > > at all.
> > >
> > > It's right here just because the &reqs[i] will never be NULL in our case.
> > > But if you see
> > >
> > > "virtio_i2c_complete_reqs" as an independent function, you need to check the
> > >
> > > req. From the perspective of the callee, you can't ask the caller always
> > > give you
> > >
> > > the non-NULL parameters.
> > We need to keep this driver optimized in its current form. If you see your own
> > argument here, then why don't you test vq or msgs for a valid pointer ? And even
> > reqs.
> >
> > If we know for certain that this will never happen, then it should be optimized.
> > But if you see a case where reqs[i] can be NULL here, then it would be fine.
> > ot the driver. And we don't need to take care of that.
>
>
> This is still not enough to convince me.  So I won't change them for now
> until I see it
>
> is the consensus of the majority.

Do you see reqs[i] to ever be NULL here ? If not, then if (req) is like if
(true).

Why would you want to have something like that ?

--
viresh

\
 
 \ /
  Last update: 2021-07-05 08:31    [W:0.057 / U:0.188 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site