| Message ID | 20241123235432.821220-1-forst@pen.gy |
|---|---|
| State | New |
| Headers | show |
| Series | [net,v3,1/6] usbnet: ipheth: break up NCM header size computation | expand |
On 2024-11-28 10:16, Paolo Abeni wrote: > On 11/24/24 00:54, Foster Snowhill wrote: >> Originally, the total NCM header size was computed as the sum of two >> vaguely labelled constants. While accurate, it's not particularly clear >> where they're coming from. >> >> Use sizes of existing NCM structs where available. Define the total >> NDP16 size based on the maximum amount of DPEs that can fit into the >> iOS-specific fixed-size header. >> >> Fixes: a2d274c62e44 ("usbnet: ipheth: add CDC NCM support") >> Signed-off-by: Foster Snowhill <forst@pen.gy> > > This change is not addressing any real issue, it just makes the > following ones simpler, right? > > If so, I think it's better to drop the fixes tag here and add the above > reasoning. Correct, this doesn't fix any real issue. It has two purposes: * Make it clearer for the reader where the numeric constants come from. * Like you said, make subsequent changes simpler by introducing intermediate constants that are used by subsequent patches. Ack, will remove the "Fixes" tag and add the above description to justify the change. >> --- >> Each individual patch in the v3 series tested with iPhone 15 Pro Max, >> iOS 18.1.1: compiled cleanly, ran iperf3 between phone and computer, >> observed no errors in either kernel log or interface statistics. > > This should go in the cover letter (currently missing, please add it in > the next iteration). Agreed, will add a cover letter for v4. Depending on the outcome of the comments/discussion on patch 4/6 in the series ("usbnet: ipheth: use static NDP16 location in URB") will likely reiterate the explanation of why I approached the changes the way I did. I think it provides important context, and also points at a potential way to enhance the driver to make it more flexible in case of possible future changes to iOS.
diff --git a/drivers/net/usb/ipheth.c b/drivers/net/usb/ipheth.c index 46afb95ffabe..2084b940b4ea 100644 --- a/drivers/net/usb/ipheth.c +++ b/drivers/net/usb/ipheth.c @@ -61,7 +61,18 @@ #define IPHETH_USBINTF_PROTO 1 #define IPHETH_IP_ALIGN 2 /* padding at front of URB */ -#define IPHETH_NCM_HEADER_SIZE (12 + 96) /* NCMH + NCM0 */ +/* On iOS devices, NCM headers in RX have a fixed size regardless of DPE count: + * - NTH16 (NCMH): 12 bytes, as per CDC NCM 1.0 spec + * - NDP16 (NCM0): 96 bytes, of which + * - NDP16 fixed header: 8 bytes + * - maximum of 22 DPEs (21 datagrams + trailer), 4 bytes each + */ +#define IPHETH_NDP16_MAX_DPE 22 +#define IPHETH_NDP16_HEADER_SIZE (sizeof(struct usb_cdc_ncm_ndp16) + \ + IPHETH_NDP16_MAX_DPE * \ + sizeof(struct usb_cdc_ncm_dpe16)) +#define IPHETH_NCM_HEADER_SIZE (sizeof(struct usb_cdc_ncm_nth16) + \ + IPHETH_NDP16_HEADER_SIZE) #define IPHETH_TX_BUF_SIZE ETH_FRAME_LEN #define IPHETH_RX_BUF_SIZE_LEGACY (IPHETH_IP_ALIGN + ETH_FRAME_LEN) #define IPHETH_RX_BUF_SIZE_NCM 65536
Originally, the total NCM header size was computed as the sum of two vaguely labelled constants. While accurate, it's not particularly clear where they're coming from. Use sizes of existing NCM structs where available. Define the total NDP16 size based on the maximum amount of DPEs that can fit into the iOS-specific fixed-size header. Fixes: a2d274c62e44 ("usbnet: ipheth: add CDC NCM support") Signed-off-by: Foster Snowhill <forst@pen.gy> --- Each individual patch in the v3 series tested with iPhone 15 Pro Max, iOS 18.1.1: compiled cleanly, ran iperf3 between phone and computer, observed no errors in either kernel log or interface statistics. v3: * NDP16 header size is computed from max DPE count constant, not the other way around. * Split out from a monolithic patch in v2. v2: https://lore.kernel.org/netdev/20240912211817.1707844-1-forst@pen.gy/ No code changes. Update commit message to further clarify that `ipheth` is not and does not aim to be a complete or spec-compliant CDC NCM implementation. v1: https://lore.kernel.org/netdev/20240907230108.978355-1-forst@pen.gy/ --- drivers/net/usb/ipheth.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)