read_packet(9)

💅 read_packet(9) — the kernel API manual, bestie edition 🎀

okay so this one is from the kernel API manual, section 9 — the driver-interface girlies know 💅. Today we're looking at read_packet, and honestly? She's a workhorse. Let's get into it.

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✨ NAME ✨

read_packet — transfer 1 packet from an OUT endpoint into request 🌸

Like, exactly one packet. Not two. Not "however many fit." One. periodt.

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🦋 SYNOPSIS 🦋

int read_packet (struct pxa_ep *ep , struct pxa27x_request *req );

That's her signature. That's the whole vibe. Returns an int, takes two pointers, no cap.

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👑 ARGUMENTS 👑

• ep — pxa physical endpoint 💜
• req — usb request ✨

Two besties, one job. ep is where the bytes are coming from, req is where they're going to.

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🌈 DESCRIPTION 🌈

okay so here's the tea 🍓: read_packet takes bytes from an OUT endpoint and transfers them into the usb request. That's it. That's the function.

But here's the part you actually need to remember, so listen up 🔥: if there is less space in the request than there are bytes received in the OUT endpoint, the extra bytes are left in the OUT endpoint. They don't get dropped, they don't get silently truncated into the void — they just chill there in the endpoint. So like, don't go assuming everything got drained, okay? 👀

And then — this is the main character moment — it returns how many bytes were actually transferred. Not how many you asked for. Not how many were sitting in the endpoint. How many actually made it. Read the return value, bestie. It's giving "I'm telling you the truth, please listen." 😭

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💀 SEE ALSO 💀

okay so the kernel file this lives in is ./drivers/usb/gadget/udc/pxa27x_udc.c, and the related-girlies list is long. Like, genuinely long. But we don't skip entries in this house 🫶 — here's every single one:

• is_match_usb_pxa(9), find_pxa_ep(9), update_pxa_ep_matches(9), pio_irq_enable(9), pio_irq_disable(9), udc_set_mask_UDCCR(9), udc_clear_mask_UDCCR(9), ep_write_UDCCSR(9), ep_count_bytes_remain(9), ep_is_empty(9), ep_is_full(9), epout_has_pkt(9)
• set_ep0state(9), ep0_idle(9), inc_ep_stats_reqs(9), inc_ep_stats_bytes(9), pxa_ep_setup(9), pxa_eps_setup(9), pxa_ep_alloc_request(9), pxa_ep_free_request(9), ep_add_request(9), ep_del_request(9), req_done(9), ep_end_out_req(9), ep0_end_out_req(9), ep_end_in_req(9), ep0_end_in_req(9), nuke(9)
• write_packet(9), read_fifo(9), write_fifo(9), read_ep0_fifo(9), write_ep0_fifo(9), pxa_ep_queue(9), pxa_ep_dequeue(9), pxa_ep_set_halt(9), pxa_ep_fifo_status(9), pxa_ep_fifo_flush(9), pxa_ep_enable(9), pxa_ep_disable(9)
• dplus_pullup(9), pxa_udc_get_frame(9), pxa_udc_wakeup(9), should_enable_udc(9), should_disable_udc(9), pxa_udc_pullup(9), pxa_udc_vbus_session(9), pxa_udc_vbus_draw(9), pxa_udc_phy_event(9), udc_disable(9), udc_init_data(9), udc_enable(9), pxa27x_udc_start(9), stop_activity(9), pxa27x_udc_stop(9)
• handle_ep0_ctrl_req(9), handle_ep0(9), handle_ep(9), pxa27x_change_configuration(9), pxa27x_change_interface(9), irq_udc_suspend(9), irq_udc_resume(9), irq_udc_reconfig(9), irq_udc_reset(9), pxa_udc_irq(9), pxa_udc_probe(9), pxa_udc_remove(9), pxa_udc_suspend(9), pxa_udc_resume(9)

Yeah. Sixty-nine cross-references. She's connected. iykyk 💅✨

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ngl the whole list is worth a scroll if you're poking around the pxa27x gadget driver — it's basically the entire neighborhood 🏘️

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alright bestie, that's the page 💖 — brought to you from ./drivers/usb/gadget/udc, dated October 2026. mwah, go read your packets responsibly 🎀🦋💜