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Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Andrew Lunn , Gerd Hoffmann , Vivek Kasireddy , Sumit Semwal , Christian =?iso-8859-1?Q?K=F6nig?= , Shuah Khan , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, linux-kselftest@vger.kernel.org, sdf@fomichev.me, razor@blackwall.org, daniel@iogearbox.net, almasrymina@google.com, matttbe@kernel.org, skhawaja@google.com, dw@davidwei.uk, Joe Damato , Bobby Eshleman Subject: Re: [PATCH net-next v5 1/3] net: devmem: allow rx-buf-size > PAGE_SIZE per dmabuf binding Message-ID: References: <20260708-tcpdm-large-niovs-v5-0-34bf6fac941b@meta.com> <20260708-tcpdm-large-niovs-v5-1-34bf6fac941b@meta.com> <20260721110713.325d36ba@kernel.org> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260721110713.325d36ba@kernel.org> On Tue, Jul 21, 2026 at 11:07:13AM -0700, Jakub Kicinski wrote: > On Wed, 08 Jul 2026 15:55:04 -0700 Bobby Eshleman wrote: > > diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml > > index 5f143da7458c..70b902008bd3 100644 > > --- a/Documentation/netlink/specs/netdev.yaml > > +++ b/Documentation/netlink/specs/netdev.yaml > > @@ -598,6 +598,13 @@ attribute-sets: > > type: u32 > > checks: > > min: 1 > > + - > > + name: rx-buf-size > > rx-page-size, we're modeling device pages. > rx-buf-len exists in ethtool and is something else. > > > + if (info->attrs[NETDEV_A_DMABUF_RX_BUF_SIZE]) { > > + u32 rx_buf_size = nla_get_u32(info->attrs[NETDEV_A_DMABUF_RX_BUF_SIZE]); > > + > > + if (!rx_buf_size || !is_power_of_2(rx_buf_size) || > > + rx_buf_size < PAGE_SIZE) { > > we should add a check: min: page-size in the Netlink policy? I played around with this adding: Documentation/netlink/specs/netdev.yaml: definitions: + - + type: const + name: page-size + value: 4096 # dummy value, to pass ynl_gen_c.py checks + header: asm/page.h + scope: kernel Generating: +static const struct netlink_range_validation netdev_a_dmabuf_rx_page_size_range = { + .min = PAGE_SIZE, + .max = U32_MAX, +}; + ... but the dummy 4096 is kind of annoying. ynl_gen_c.py can't know the value of PAGE_SIZE but needs some value for its arithmetic checks (e.g., confirm min < max is true). Should we stick with using a dummy value, or should we add a patch teaching ynl_gen_c.py to allow value-less consts (skip the arithmetic checks)? Best, Bobby > > > + NL_SET_ERR_MSG_FMT(info->extack, > > + "rx_buf_size %u must be a power of 2 >= page size (%lu)", > > + rx_buf_size, PAGE_SIZE); > > This must point at _ATTR, the _FMT is unnecessary. > -- > pw-bot: cr