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([2001:a61:1394:8401:ac5f:98de:4c1b:7bf1]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3997f9b260fsm19622638f8f.43.2025.03.27.06.21.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Mar 2025 06:21:18 -0700 (PDT) Content-Type: multipart/mixed; boundary="------------Aw0jc0aBmLeCrRJ7u0mnJ0i9" Message-ID: <42118b9b-7aa1-4559-824a-2c2ec70ea7d8@suse.com> Date: Thu, 27 Mar 2025 14:21:18 +0100 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Handling incoming ZLP in cdc-wdm To: Robert Hodaszi , linux-usb@vger.kernel.org References: Content-Language: en-US From: Oliver Neukum In-Reply-To: This is a multi-part message in MIME format. --------------Aw0jc0aBmLeCrRJ7u0mnJ0i9 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi, On 26.03.25 16:50, Robert Hodaszi wrote: > The problem is, wdm_poll() always return with EPOLLIN even when wdm_in_callback() receives a ZLP, as it sets WDM_READ. So it makes sense for glib to think, there's a pending packet. In wdm_read(), if the packet's length is 0 (desc->length = 0) and WDM_READ is set, we reach > > if (!desc->length) > > line, where it puts out another URB (as the resp_count is not 0), clear WDM_READ and go back to "retry". The second time we test WDM_READ, it is obviously not set yet, and as we are reading non-blocking, the function returns with EAGAIN. Arguably the interrupt handler should set the flag for a readable result only if indeed there is data in the buffer. Could you try the attached patch? Regards Oliver --------------Aw0jc0aBmLeCrRJ7u0mnJ0i9 Content-Type: text/x-patch; charset=UTF-8; name="0001-usb-cdc-wdm-check-for-zero-length-response.patch" Content-Disposition: attachment; filename="0001-usb-cdc-wdm-check-for-zero-length-response.patch" Content-Transfer-Encoding: base64 RnJvbSA0NzMxMWUzNGNhZDFjYzEzYWI1ZDJmYmFlMjM5ZjE4OGE2ZTgyYzFkIE1vbiBTZXAg MTcgMDA6MDA6MDAgMjAwMQpGcm9tOiBPbGl2ZXIgTmV1a3VtIDxvbmV1a3VtQHN1c2UuY29t PgpEYXRlOiBUaHUsIDI3IE1hciAyMDI1IDE0OjE3OjQ1ICswMTAwClN1YmplY3Q6IFtQQVRD SF0gdXNiOiBjZGMtd2RtOiBjaGVjayBmb3IgemVybyBsZW5ndGggcmVzcG9uc2UKCldlIHNo b3VsZCBub3QgaW5kaWNhdGUgdGhhdCB0aGVyZSdzIGEgcmVzcG9uc2UgaWYgd2UgaGF2ZSBu bwpkYXRhIGluIHRoZSBidWZmZXIuCgpTaWduZWQtb2ZmLWJ5OiBPbGl2ZXIgTmV1a3VtIDxv bmV1a3VtQHN1c2UuY29tPgotLS0KIGRyaXZlcnMvdXNiL2NsYXNzL2NkYy13ZG0uYyB8IDIg KysKIDEgZmlsZSBjaGFuZ2VkLCAyIGluc2VydGlvbnMoKykKCmRpZmYgLS1naXQgYS9kcml2 ZXJzL3VzYi9jbGFzcy9jZGMtd2RtLmMgYi9kcml2ZXJzL3VzYi9jbGFzcy9jZGMtd2RtLmMK aW5kZXggODZlZTM5ZGIwMTNmLi44NTY0ODhhN2NiNmIgMTAwNjQ0Ci0tLSBhL2RyaXZlcnMv dXNiL2NsYXNzL2NkYy13ZG0uYworKysgYi9kcml2ZXJzL3VzYi9jbGFzcy9jZGMtd2RtLmMK QEAgLTIzNiw2ICsyMzYsOCBAQCBzdGF0aWMgdm9pZCB3ZG1faW5fY2FsbGJhY2soc3RydWN0 IHVyYiAqdXJiKQogCQkgKi8KIAkJc2NoZWR1bGVfd29yaygmZGVzYy0+c2VydmljZV9vdXRz X2ludHIpOwogCX0gZWxzZSB7CisJCWlmICghZGVzYy0+bGVuZ3RoKQorCQkJZ290byBvdXQ7 CiAJCXNldF9iaXQoV0RNX1JFQUQsICZkZXNjLT5mbGFncyk7CiAJCXdha2VfdXAoJmRlc2Mt PndhaXQpOwogCX0KLS0gCjIuNDkuMAoK --------------Aw0jc0aBmLeCrRJ7u0mnJ0i9--