[PATCH] pwm: imx27: workaround of the pwm output bug
kernel test robot
lkp at intel.com
Fri Dec 29 18:01:55 PST 2023
Hi,
kernel test robot noticed the following build warnings:
[auto build test WARNING on thierry-reding-pwm/for-next]
[also build test WARNING on linus/master v6.7-rc7 next-20231222]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/pratikmanvar09-gmail-com/pwm-imx27-workaround-of-the-pwm-output-bug/20231229-143435
base: https://git.kernel.org/pub/scm/linux/kernel/git/thierry.reding/linux-pwm.git for-next
patch link: https://lore.kernel.org/r/20231229063013.1786-1-pratikmanvar09%40gmail.com
patch subject: [PATCH] pwm: imx27: workaround of the pwm output bug
config: arm-randconfig-r133-20231230 (https://download.01.org/0day-ci/archive/20231230/202312300907.RGtYsKxb-lkp@intel.com/config)
compiler: clang version 18.0.0git (https://github.com/llvm/llvm-project 8a4266a626914765c0c69839e8a51be383013c1a)
reproduce: (https://download.01.org/0day-ci/archive/20231230/202312300907.RGtYsKxb-lkp@intel.com/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp at intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202312300907.RGtYsKxb-lkp@intel.com/
sparse warnings: (new ones prefixed by >>)
>> drivers/pwm/pwm-imx27.c:303:26: sparse: sparse: incorrect type in assignment (different base types) @@ expected unsigned int [usertype] sar_last @@ got restricted __le32 [usertype] @@
drivers/pwm/pwm-imx27.c:303:26: sparse: expected unsigned int [usertype] sar_last
drivers/pwm/pwm-imx27.c:303:26: sparse: got restricted __le32 [usertype]
>> drivers/pwm/pwm-imx27.c:304:29: sparse: sparse: incorrect type in assignment (different base types) @@ expected unsigned int [usertype] sar_current @@ got restricted __le32 [usertype] @@
drivers/pwm/pwm-imx27.c:304:29: sparse: expected unsigned int [usertype] sar_current
drivers/pwm/pwm-imx27.c:304:29: sparse: got restricted __le32 [usertype]
vim +303 drivers/pwm/pwm-imx27.c
219
220 static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm,
221 const struct pwm_state *state)
222 {
223 unsigned long period_cycles, duty_cycles, prescale, counter_check, flags;
224 struct pwm_imx27_chip *imx = to_pwm_imx27_chip(chip);
225 void __iomem *reg_sar = imx->mmio_base + MX3_PWMSAR;
226 __force u32 sar_last, sar_current;
227 struct pwm_state cstate;
228 unsigned long long c;
229 unsigned long long clkrate;
230 int ret;
231 u32 cr, timeout = 1000;
232
233 pwm_get_state(pwm, &cstate);
234
235 clkrate = clk_get_rate(imx->clk_per);
236 c = clkrate * state->period;
237
238 do_div(c, NSEC_PER_SEC);
239 period_cycles = c;
240
241 prescale = period_cycles / 0x10000 + 1;
242
243 period_cycles /= prescale;
244 c = clkrate * state->duty_cycle;
245 do_div(c, NSEC_PER_SEC);
246 duty_cycles = c;
247 duty_cycles /= prescale;
248
249 /*
250 * according to imx pwm RM, the real period value should be PERIOD
251 * value in PWMPR plus 2.
252 */
253 if (period_cycles > 2)
254 period_cycles -= 2;
255 else
256 period_cycles = 0;
257
258 /*
259 * Wait for a free FIFO slot if the PWM is already enabled, and flush
260 * the FIFO if the PWM was disabled and is about to be enabled.
261 */
262 if (cstate.enabled) {
263 pwm_imx27_wait_fifo_slot(chip, pwm);
264 } else {
265 ret = pwm_imx27_clk_prepare_enable(imx);
266 if (ret)
267 return ret;
268
269 pwm_imx27_sw_reset(chip);
270 }
271
272 /*
273 * This is a limited workaround. When the SAR FIFO is empty, the new
274 * write value will be directly applied to SAR even the current period
275 * is not over.
276 * If the new SAR value is less than the old one, and the counter is
277 * greater than the new SAR value, the current period will not filp
278 * the level. This will result in a pulse with a duty cycle of 100%.
279 * So, writing the current value of the SAR to SAR here before updating
280 * the new SAR value can avoid this issue.
281 *
282 * Add a spin lock and turn off the interrupt to ensure that the
283 * real-time performance can be guaranteed as much as possible when
284 * operating the following operations.
285 *
286 * 1. Add a threshold of 1.5us. If the time T between the read current
287 * count value CNR and the end of the cycle is less than 1.5us, wait
288 * for T to be longer than 1.5us before updating the SAR register.
289 * This is to avoid the situation that when the first SAR is written,
290 * the current cycle just ends and the SAR FIFO that just be written
291 * is emptied again.
292 *
293 * 2. Use __raw_writel() to minimize the interval between two writes to
294 * the SAR register to increase the fastest pwm frequency supported.
295 *
296 * When the PWM period is longer than 2us(or <500KHz), this workaround
297 * can solve this problem.
298 */
299 if (duty_cycles < imx->duty_cycle) {
300 c = clkrate * 1500;
301 do_div(c, NSEC_PER_SEC);
302 counter_check = c;
> 303 sar_last = cpu_to_le32(imx->duty_cycle);
> 304 sar_current = cpu_to_le32(duty_cycles);
305
306 spin_lock_irqsave(&imx->lock, flags);
307 if (state->period >= 2000) {
308 while ((period_cycles -
309 readl_relaxed(imx->mmio_base + MX3_PWMCNR))
310 < counter_check) {
311 if (!--timeout)
312 break;
313 };
314 }
315 if (!(MX3_PWMSR_FIFOAV &
316 readl_relaxed(imx->mmio_base + MX3_PWMSR)))
317 __raw_writel(sar_last, reg_sar);
318 __raw_writel(sar_current, reg_sar);
319 spin_unlock_irqrestore(&imx->lock, flags);
320 } else
321 writel(duty_cycles, imx->mmio_base + MX3_PWMSAR);
322
323 writel(period_cycles, imx->mmio_base + MX3_PWMPR);
324
325 /*
326 * Store the duty cycle for future reference in cases where the
327 * MX3_PWMSAR register can't be read (i.e. when the PWM is disabled).
328 */
329 imx->duty_cycle = duty_cycles;
330
331 cr = MX3_PWMCR_PRESCALER_SET(prescale) |
332 MX3_PWMCR_STOPEN | MX3_PWMCR_DOZEN | MX3_PWMCR_WAITEN |
333 FIELD_PREP(MX3_PWMCR_CLKSRC, MX3_PWMCR_CLKSRC_IPG_HIGH) |
334 MX3_PWMCR_DBGEN;
335
336 if (state->polarity == PWM_POLARITY_INVERSED)
337 cr |= FIELD_PREP(MX3_PWMCR_POUTC,
338 MX3_PWMCR_POUTC_INVERTED);
339
340 if (state->enabled)
341 cr |= MX3_PWMCR_EN;
342
343 writel(cr, imx->mmio_base + MX3_PWMCR);
344
345 if (!state->enabled)
346 pwm_imx27_clk_disable_unprepare(imx);
347
348 return 0;
349 }
350
--
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